It's only the older aircraft(AS355, Bo105) that need a warm up period. Certainly the EC135, and probably the 902 as well, do not have a warm up period. The only thing that delays us in our 135 is waiting for the EFIS screens to come on line. Even in our old Squirrel, we could be airbourne within 2 minutes of me running out of the office door.
North Wales' 135 has standard flight instruments, so can probably get airbourne a bit quicker.