The most important part of using Sretch Bolts is to pay attention to having a uniform sequence on the called for 'snug torque' specs. This is as important as the angle spec. as it creates the baseline for the latter.

I think the resting period you mention may be to let the bolts stabilize between sequence as they heat up when streached.

Here is the basic info:
http://www.robbos.com.au/myweb/Tech_Bolts.htm