If you need the minimum snipe time, then you can have it low to 1 second. I personally would recommend to use somewhere between 6 and 10 seconds to get around possible network delays.
If you need the time when you can activate your snipe (enter auction id, enter your snipe amount and activate it), then it must be done a few minutes in advance so system will have enough time to schedule it:
http://www.myibay.com/login/faq/4/#q5