Spawns can last for weeks, given that the conditions don't stay stable over a shorter period of time. With this yo-yo weather situation, it's likely that they will "try" & come in, & get pushed off, try again, etc. They will continue to move in & out until the water temps are such that any further attempt would be pointless ... and they'll consume the eggs (for their own survival).
In a perfect world, under perfect conditions (water level/water temps/stable weather) ... it wouldn't take, all those mature enough to spawn, more than a week to spawn out.
Unfortunately, we don't have perfect conditions ... so the fish will adapt, and continue trying to spawn until their instincts tell them it's fruitless. That may be a problem for the fish ... but not necessarily for the anglers, as it does spread the timeframe of them being shallow over a longer period of time. Can you imagine what Crappie fishing during the spawn would be like, if they all came in to spawn within a few days time
... cp