Another word could be era.
instead of long period of time, you can use phrases like:a long terma long spella phaseyou can even use the word tenure if it suits the situation.
Regime is the obvious word. It would be nice to think of others.
Anachronistic.
* Bell time is the time for bell. Like, when it's dismissal or a start of another period. Or, when it's lunch.
the word war did not exist in that time period the prehistoric era was a time when the was no written documents
AGE.
exposure time = induction period
For a while can be used to mean 'for a short period of time'.
exposure time = induction period
Age, era, period of time etc.
interval, lapse of time, period, span, stretch, timespan.
Era Eon Epoch Forty days & forty nights Forever
instead of long period of time, you can use phrases like:a long terma long spella phaseyou can even use the word tenure if it suits the situation.
distance, width, length, extent, area, time, duration, limit, period
Analyze, monitor, keep track of
in another space of time
A period of time is commonly called an era.