I hate to say it but mixing rigs like that often aren't very efficient, so you'll have to watch and judge your system yourself. (The flow is all at the top but the salt naturally settles to the bottom.)
Under good mixing Reef Crystals can be ready in 5-10 minutes – as soon as it's clear all through. Time how long your takes!
I would not heat the saltwater unless you were doing a 100% water change with it. Precipitation onto the heater (and the mixing pump for that matter) is likely, especially if the heat sources are left on for a long period.
I mix without heat, using nothing but a mixing paddle.
In my Water thread I tested a bunch of mixing configurations, including my hands, a paddle, airstones and multiple kinds of pumps.
In post
#301 I showed the mixing paddle method. Ready in 5 minutes.
In post
#306 I showed the best pump mixing method. Ready in 5 minutes.
That was 5 gallons....I mix in a 55 gallon olive barrel now for 50% water changes instead of 5% like in that thread.
55 gallons does take longer than 5 min, but not much longer! (If I can remember, I'll time the paddle mixing next time around.)
The paddle is 100% easier and simpler, BTW. No setup, no power cord! No pump to accidentally run dry.
