PH meter question

I broke down and bought a PH meter and I used it this past weekend. My question is when do you take the reading? I waited 10 minutes to take a sample. I cooled the sample down to 71 degrees and I got a reading of 5.4 but then the PH started to climb slowly. After about 5 minutes the sample got up to 6 so I added some more Latic acid to the mash to be safe. I was mashing 10 lbs of 2 row and 12 ounces of crystal 15.

I just started using a ph meter too. I assumed that after thoroughly mixed would be the first measurement. Hearing that yours climbed throughout mash, I will measure every 15 i suppose. I used phosphoric acid to lower. Didn't see much of an effect though. Used a capful on a 20lb mash. I think that I am going to start usind saurmalz to lower ph from now on. Without any adjustment however, I was at 5.4. Target is 5.2-5.5. To be honest I was surprised that it was in the target range with no adjustments.