All the work in measuring pH is calibrating the meter. Once that is done each additional measurement is very little effort. So take readings frequently i.e. just after dough in and perhaps every 10 minutes after that. You will soon learn how long it takes the measurements to stabilize in the beers you brew.
I will note that when sauermalz is being used that it seems to take longer for the readings to stabilize. They can be alarmingly low at dough-in but then drift up over the course of half an hour or so.
The goal is, of course, to have the pH reading be a confirmatory check that all is OK - not a warning that something needs to be fixed. At first, naturally, that will be the case but as you learn your way it won't.