8 Weeks is not too soon. The typical range is 6 weeks to 3 months. The main objective of early testing is to make sure the initial PSA is <0.1, in other words, there isn't obvious persistent PSA and that the surgery achieved it's main purpose without significant PSA sources being left behind. I would suggest you request that you ask your doc to be followed with an ultrasensitive PSA test -- preferably Labcorp's 3-decimal test, otherwise Quest's "post-prostatectomy" 2-decimal test. This testing will allow you to track better your absolute numbers as well as any upward trend. (The lower limit of Labcorp's uPSA test is now <0.014; that for Quest is <0.02. Labcorp raised its lower limit, which used to be <0.006. The downside is that with a <0.014 result you can't know whether your nadir is below 0.01.)
Another advantage of uPSA testing for higher-risk men with adverse post-op path is to learn your PSA nadir. This usually occurs within the first few months. Several studies have shown that whether your nadir is above or below a threshold is statistically correlated with your chances of remaining BCR-free. A nadir below 0.03 is good; below 0.01 better. The right-most digit of any test holds uncertainty, so rounding the 3-decimal Labcorp test to 2 decimal places is probably more reliable than a 2-decimal test. Keep in mind that very low PSA levels can fluctuate for both intrinsic reasons (you) and extrinsic ones (sample prep, test reagents, equipment calibration, etc.) -- another reason it's good to round to a 3-decimal result to 2 places -- peace of mind
Lastly, some higher-risk men may want to start adjuvant or salvage therapy at a PSA below the "official" BCR definition of PSA 0.2 and rising (perhaps 0.1). A uPSA test gives you more lead time to both monitor your values and trend and set up a plan for any further therapy.
Note that all this fuss over uPSA testing is aimed at men at higher risk. Most G6 (3+3) men are happy to get their periodic <0.1 results using a PSA designed for men with prostates.