in terms of pain lasting, for me it seems to be more about my mental space or other factors that are harder to predict rather than how hard, or even if there is bruising. i've had bruises that i didn't notice, or times with no bruising when my back side was tender as could be.
i find that the less warm-up, the more likely the pain is to linger, so that's a consideration.
as for how long i've had to wait... i think i had to wait a week or more last spring for a (non-spanking) punishment to be delivered. w was furious with me for the infraction, and wanted to cool off before she gave the punishment. that one was hard.
however, similar to t, often times if w delays a punishment, she forgets to give it at all, and that is frustrating. we've got a rule at this point where if i have to remind her (courteously and appropriately) more than three times, i don't need to be punished for that offense. it's happened that way several times since the rule was instituted. but that works out better for me, personally, than having to remind her repeatedly, suspecting strongly that if i didn't say anything, i would avoid the punishment.