I've experienced no difference doing it either way, although I have a recirculating system. If you think you may need to adjust pH you should test earlier as conversion happens rather quickly.
Are you using mash pH software and using acid to get in to the target range before you dough in?
Yes use Brun & check with AD12 meter
I have 1 infusion esky & have been taking samples cooled to 22c about 15 - 20 mins in
I have never adjusted on the run as the Brun software is very close
I just adjust the next time with more or less acid malt
Going to recirc system 1v & was just wondering ?
While ceryain enzyme activity is optimised at certain pH ranges, it's impossible and likely overkill to be making adjustments that minutely. You also should be taking the sample at room temp anyway.
Personally, I'd take one at 55, another at sacch just to see how things behave and use that info in software to predict/tweak on an ongoing basis.
Good tip will take several readings
If I take a reading too far into the mash time wise the PH goes down ?
Will have to take a few readings after mash before the boil & after the boil also to see how I'm going