This is how I determine pouring temp.
You have to watch the ingots melt in the crucible. When the last piece melts, start a timer.
I posted this on another thread.
I've learned from experience pouring different sized objects, that one temperature does not give the same finish or fill. I use 'time after the last charge melts'. Heavy thick pieces get 1 minute, longer thin pieces get 2 minutes, the most I've done was 3 minutes and that was because 2:45 seconds gave me a cold shut. No flux with clean ingots, no degas, just skim and pour.
The cooler the metal, the better the finish and you get less shrinkage.