I've played Gmod Jailbreak many times, if you'd like, I could help out. I'm not asking for admin, just offering to build, event, and do other stuff.
There should be no time limit. Really. Guards win every time.
The issue with that is that when you're dead those eight minutes feel like forever and people leave. Sitting there dead while watching people sucks. I do agree that maybe it could be raised a bit but I dunno.
However, one thing to consider is that games like these, requiring a bunch of 'regular players' who know all the rules of being guards, barely even work on communities like Counter Strike where the community is like 14-18. Expect to water down your game substantially so it'll work with the younger Blockland audience.
Poll