I logged in when the timer was still at 20 minutes, and a slime had spawned quite some time before that (about half hp with not too many attacking it, so 10-15 minutes probably).
it was close to accurate (only off by a few minutes) for the third spawn today. I would be willing to bet this has to do with the first slime being manually spawned by GMs.
It should have only been off for the slime that spawned 4 hours after the server turned on. This is because it automatically spawned when turned on, and the GM's killed it to spawn 10-15 mins later so people had time to set up their shops and get organised. So if the first slime spawned 15 minutes after the server was turned on, the next one would have spawned 3 hours 45 minutes later although the timer would have said 15 minutes to go.
