I think the issue as with most things on the server is that there's some people that abuse anything they can; if you reduce prison times too much, people will evade 20 times in a day just to troll around.
If we don't mind dropping the realism and leaning into the game and having fun, I'd suggest a more smart reduction: for the first time you get sent in DOC in 7 days, you get 90% of the time reduced.
This would mean that if you rarely get arrested, you don't have to spend much time there, but if you want to abuse the reduction, you won't be able to more than once a week.