Maybe I need to go back to borates pool school but I am fairly sure the ph change from the acid should show on a test within half to an hour or so of mixing. You don't have to wait 48 hours to test for it.
As far as borate testing, I would assume that your borate level is close to where you intended it to be. If you used the pool calculator, testing for it is just to confirm the result. The test is a strip, and it really can't tell you exactly how much above or below 50ppm you are anyway. For now, like CYA you assume what you added is in there.
PH should be addressed regardless of borate level. Verify your acid percentage if the amount you used did not equal what the calculator said it should do. I can't locate 31% here, mine is <25% and that's not an option on the calculator so we have to adjust it a bit.
Insofar as how to determine how high it is, you really can't so easily till it comes down a bit. Do the acid in increments and see when it changes enough to show on the test.