We are entrained to 24 hours by our environment. Jet lag is replaced at about 45mins per day. It has inputs from the visual system, plus some from the pineal gland. Flashes of 1msec look equal in duration to those up to 60-70msec. Notably, Eriksen finds, it is efficient for short term visual memory to insert up to a 25msec delay between 2 items, presented sequentially, that subjects are asked to combine into one pattern.
Longer delays interfere with our attempts to combine the items.
Drugs affect perceived duration. If unfamiliar items are presented, their duration seems longer than if familiar items are presented. If we estimate duration after the event the estimate will be shorter than if we attend and estimate while the event is on. This could because the baseline we use keeps getting bigger.