The PH test should be read immediately. The color will often shift if you leave it sitting for a few minutes. The CYA test is good for perhaps ten minutes after mixing, especially if you shake it up a bit right before reading.
The CYA test is not affected by high temperatures (within reason). Low temperatures can slow down the chemical reaction, so it doesn't complete, leading to less cloudiness than there ought to be. But anything around 70 or above should allow the reaction to run to completion and give the same results.