I do the ‘pump before date’ thing as well, depending how long and how much pressure, the temporary size will last maybe 4-5 hours.
Here is an update on my own Bathmate:
I mainly use it outside of water, I fill the pump up with water and use it in my room, pumping the water back into a bowl. (Heated water, of course).
I’ve been pumping to just above my max length every session, and holding for 20 minutes. Occasionally, I do get the purple spotting if I hold too long, it quickly goes away though with re-heated water / wrap. The flaccid pump is incredibly large for maybe 30 minutes, then after that it is just slightly larger than average for a few hours.
I do see the stretch marks from the rubber rings after use, it also goes away fairly quickly though, so I’m negligent about it.
As well, I notice you MUST keep very very shaven, if there is any hair, it will disrupt the seal and air will leak into the pump.
And another thing, I’ve only had my pump for about 3-4 months, and I am seeing a slight cracking in the pressure release valve. My pump is leaking air periodically during my pump sessions. I may have to get a new one.