[Touch Diamond, MDA Compact IV General] low.flying.pigs:
Short answer:

Yes it is possible. No it is not currently implemented as at 4.12beta22 within GPS Cycle Computer. It may be implemented in the future.

Potential workaround:

In the interim, there are a range of external USB based power packs available that would extend the run time of a device. These are generally useful to have anyway. For many users, using a power pack, there would be enough capacity for the screen to remain on at all times without concern. This is generally simpler than using a dynamo to generate power. Some users utilise both.

Long Answer:

The reason the seemingly rather basic functionality is not currently implemented is because it was intended to be proposed following Exit Shutdown proposal on 28 July 2013, post 1836. However, that received immediate, inordinate, sustained and entirely disrespectful objection without cogent reason. Part of the flawed basis of objection was Shutdown could be done from the Operating System, which it can in some circumstances, as can this and other related functions, in some circumstances. Those are not however the circumstances in which the functionality would be provided for and mainly used.

Most dedicated device functionality, and indeed most feedback generally, was subsequently not then proposed and accordingly has not to date been implemented. The necessary testing and research required was also abandoned at that time. A process of gradualism is now in effect.

That has been disastrous and damaging to the project, and it remains to be seen if in fact GPS Cycle Computer actually has any future at all in active development.

It has been disastrous and damaging for all ordinary users, as dedicated devices undoubtedly are a significant part of the future of GPS Cycle Computer, assuming there is a future, given many if not the majority use their Windows Mobile device now mostly or primarily only for GPS Cycle Computer.

Furthermore, an ever increasing number of users utilise, or will in the future utilise, Windows CE based actual dedicated devices. That same individual, whom most users now regard as a troll based upon overwhelming and compelling evidence, also sought to disrupt and prevent development of GPS Cycle Computer compatibility with Windows CE.

This was done by dismissing Windows CE users, without actual cogent reason and based again either upon profound ignorance, or as users have pointed out more likely, given the troll knew exactly where and how to strike, exact knowledge of how to derail and destroy the future of the project.

The technique of questioning whether GPS Cycle Computer users needed such 'old' devices was used, when the devices in question are in fact recent or current models readily available brand new and not in any way whatsoever old or obsolete.

The technique of questioning generally whether those submitting feedback actually use GPS Cycle Computer, in an effort to prevent implementation and future submission of any feedback has also been used.

Both are known trolling techniques and devastatingly effective not just in delaying progress, but disrupting and destroying morale and community, key troll objectives.

As users have pointed out, often well meaning users will attempt to intervene having not understood properly, which is what the troll hopes for. Ideally for the troll, this in turn causes further disruption as the community, instead of uniting and turning against the troll, begins to turn on itself and fall apart and become off putting to anyone considering any kind of involvement.

This is commonly known as divide and rule. What generally happens is the active productive contributors that have driven a project forward no longer do so, and the troll remains picking off any new contributors until the project is dead, and then the troll moves on to destroy another project.

Often a troll is 'working' several projects. Sometimes a troll following scrutiny of their actions will disappear for a while hoping that will end the scrutiny enabling them to return later. Sometimes in attempt to maintain cover a troll will do whatever is necessary for that, appearing to agree with perceived leaders, apologising when exposed and contributing minimally, but contributions are always less than the trolls negative effect, to ensure a continual decline. Rarely if ever do such individuals change, as in for the better. Change is usually manipulative, intended to enable continuation regardless, as users have pointed out.

These issues have been extensively and exhaustively documented previously.

The remainder of the answer varies dependent on device and Operating System. In brief:

Windows Mobile Devices:

Dependent on version and device, via Windows Settings, there are options for back light turn off and sometimes back light dimming, after a defined period of inactivity, which can be further set dependent on whether running on internal battery or external power source.

GPS Cycle Computer, when GPS is on, will attempt to override however and always keep the back light on unless 'Safe Energy: do not keep Backlight on' in Settings > Options > GPS Screen is selected. If 'Keep touch on while back light off' is selected under Settings > Options > Main Screen, on some devices, back light can be reactivated with a tap.

From the Menu page, the 'BKlight' button switches off the back light immediately when pressed.

There are no technical reasons why as a minimum, as functionality to override Windows Mobile settings already exists, and functionality to switch off back light already exists, why in settings, a user definable time period cannot be provided in due course to operate in conjunction with existing back light off functionality.

Note: It can be observed that on some devices when pressing BKlight, it is not just the back light that is switched off. The screen can be switched off. The digitizer can be switched off, and therefore afterwards tapping the screen has no effect.

Windows CE 5 and CE 6 Devices:

Access to the minimal underlying Operating System is typically restricted and unavailable to the user. The intended dedicated application of the device typically as a minimum allows control therein of Volume, Back light Brightness and Back light off.

Where GPS Cycle Computer is running in place of that intended dedicated application, these controls are inaccessible. As implementation can be different in Windows CE, the Windows Mobile functionality detailed above does not usually work.

Potential workaround:

In the interim, some intended dedicated applications apply settings at system level, and thus would also apply to GPS Cycle Computer. Some intended dedicated applications however do not retain these settings, but apply them when running, and thus require to be running in addition to GPS Cycle Computer. This may or may not be acceptable dependent upon hardware resources. This may or may not be within the capability of a user to achieve.

There are no technical reasons why GPS Cycle Computer cannot in due course implement control of Volume, Back light Brightness and Back light off, and abundant reasons why these should be implemented, allowing Windows CE devices to be used properly, and Windows Mobile devices to be used properly as dedicated devices.

The necessary further testing and research to enable that, and correct operation of existing functionality on all devices, can be resumed if requested and an assurance is given that subject to programming capability, it would be implemented in GPS Cycle Computer. Otherwise foreseeable development efforts will continue to focus elsewhere.

Users that do not need, require, want, or will not use proposed functionality will not use it and are therefore not adversely affected, as existing functionality will not be adversely affected.

low.flying.pigs