It really depends. If you have a strong heating element (mine is 5500w) then it'll heat up rather quickly. My preboil is usually ranging from 7 - 8.5 gallons, and it really heats up to boiling in just under 8 minutes or so. I also get a pretty big boil off from that element so my PID helps...
Yes sir, the top valve is for recirculation. Toolbox is the controller obviously, but the pump pulls from the bottom valve to recirculate wort to the top of the grains. I only make 5.25 gallon batches with this rig, but it works very well. It's been pretty accurate and my efficiency has been on...