Well right now I'm still controlling the flame by hand, no PID controller. So i will be sneaking up on the mash out temp. Is there a down side to adding additional time while the temp rises. Do most just start earlier like at the 45 minute mark?
It's still easier to control HERMS (in my opinion at least) because you don't have to worry about heat stratification like you do with a direct fire system. You know, in other words, where your temps are so long as you have even a little bit of agitation to move the water around. Plus, if you overshoot you can always just turn off the pump and bring the HLT back down. It's just another layer of distance between the heat and the wort.
I wouldn't necessarily recommend starting your mahout earlier unless you are absolutely sure you are done with conversion by that point. Most starches should have converted by 45 minutes, but the extra 15 minutes just gives you a little bit of insurance in case your crush is off, etc. The extra time certainly isn't bad, except to the extent that it's an extra fifteen minutes that you have to wait. The main thing is just to be consistent in your process.