A final reading after tempering is fine for telling your customer what the blades hardness is, but it really doesn't help much in refining or troubleshooting your heat treatment. Say your final hardness is 59HRC, that sounds great but is it 59 after tempering what was only 61HRC to begin with? I have had many people just starting out, without a full understanding of what goes on inside the steel, ask what difference does it make if the end hardness is the same, but it makes a huge difference depending on what phases or structures gave you that reading; tempered martensite is the ultimate in strength and abrasion resistance, while tempered pearlite is pretty much a waste of time.
On the topic of time before temper, people tend to jump to extremes on the concept. I have seen some claim that there is no need to temper right away at all and that it will be fine whenever you can get to it, which is patently false if you properly hardened your blade. On the other hand I have heard of people being so paranoid about the temper that they are probably tempering a lot of leftover austenite in a blade that is still too warm for conversion to be complete. A Rockwell test should only take about 2 or 3 minutes to do and if a blade is cracking in that amount of time there probably is not much one could do to prevent it. If a test is take too quickly without proper cooling you will also get false readings from that same unconverted austenite. The anvil of a Rockwell tester bears little resemblance to an anvil for forging on and would only come in contact with a rather small area of the blade.
If visible cracking occurs in such a short time after the quench it would be very likely that the blade already has micro-cracking from the quench itself, and the best safeguard would be to review the severity of the quench. If there were still concerns after this, a couple of measures could be taken to relieve the problem, one would be a short “snap” temper below 350F to stabilize things, the other would be to approximate martempering by interrupting the quench at 400F and allowing the blade to air cool to room temp. Both would require an allowance for the “as-quenched” hardness. i.e. if the steel should be 65HRC it may be a couple points lower due to the snap tempering, how much would depend on your specific temper. With a proper martempering you can expect from .5 to 2 points lower as quenched due to the auto-tempering effect of the air cool, this will not be lost hardness as some people mistakenly fear, but a head start on the actual temper.
I use true martempering processes on all my blades and will even rinse the blades in cold water to insure complete transformation before taking my as-quenched readings, my confidence that there is not so much as a micro crack on fully hardened stock done this way is backed up by extensive microscopic examination.