The shortest time you can spend in a prison is around 1 year.
If your sentence is 1 year or less than you may just serve your time in a county jail and not a prison unless you have a year or 6 months left on your sentence and the jail is getting too full.
Then you may go to prison for the remainder of your sentence and could spend only 6 months or less in a prison.
Usually you stay in county jail if your sentence is a year or less.
And if your sentence is more than a year then you would be transferred to a state prison to spend your time.
If you've been in jail for 6 months or longer awaiting your prison sentence then that time would be credited and you would have that time taken off your prison sentence.
But if you're going to prison for life then the time spent in county jail doesn't mean anything because you're going to prison and will have to live there until you die.
For prisoners time must seem like it's going slow and a minute probably seems like 2 hours and an hour probably seems like 12 hours.
But time never speeds up or slows down and time always goes at the same speed for everyone no matter where they are or what they are doing.
The time seems like it's going by slowly in prison because of the boredom and the the prisoners are waiting until the time in prison is up so they can be released if they have a release date.
I imagine the time in prison for life in prison without parole prisoners goes by slowly at least for the first 10 to 20 years in prison.
Then later they get into a routine and the time just goes by without them thinking about it.
But I would imagine that if I were in prison which I never hope to be that if I was in prison sitting around doing nothing and watching a clock tick by then the time would drag.