As a reference point, my well water runs in the mid-fifties year 'round. Beyond that, I try not to waste gas by heating the air around my HLT, plus I really don't want to warp the bottoms of my Boilermakers anyway, so I try to heat at what might appear to be a leisurely pace. All that taken into account, bringing ~8 gallons to strike temp typically takes around 40 minutes.
My Boilermakers came with a sheet of stainless steel that I stick one long edge between the edge of the kettles and the pot rests, protecting both the ball valve/male camlock fitting and the sight gauge from heat. This has worked very well indeed, such that the vinyl cover over the ball valve lever is still pristine after a couple of years of brewing...
hth
Cheers!