Corrections Act 2004, s 69-78
This will depend on the circumstances. The more urgent a situation is, the more likely that it might become reasonable for some minimum entitlements to be removed. At the same time, the more urgent the situation is, the more likely that the restrictions will be more temporary.
For example, if there was a fire in the prison, you may have to be moved to another area of the prison where you are unable to exercise, or to have visitors while the fire is being brought under control. This should be for no longer than necessary. If the exercise yard was damaged in the fire, it would not be reasonable for the prison to remove your right to exercise until a new yard was built. Instead, the prison would have to find new ways to provide your minimum entitlement to have at least 1 hour of exercise per day in the open air.
If there was a health and safety issue, like a contagious virus, it may be reasonable to urgently change the way things are done, which may involve some temporary restrictions on minimum entitlements. However, the prison has an obligation to find new ways to provide your minimum entitlements.