Add a roundtime cap for sleeper agents

[Lord_earthfire]

i would say don't make antag spawn like 5 minutes before the shuttle gets auto-called. Very often that late into the round people are fully geared up or their projects are dying out, so giving it a nice little boost by misusing their project for antagging gets kinda nice. I remember killing someone with dreamsickle eggs by cold/sugr overdose just because i had them in the moment i rolled sleeper.

Sleeper agent is very often "hey, i get to betray the person i was RP'ing with the whole shift" and these moments are awesome.