I have both my PowerWalls and both Tesla cars charge during my overnight Off Peak cheap rate (for me its a fixed time during the night, rather than a variable one; I presume yours is the same)
I set the car to charge using the car scheduler. I set the START time (which will mean that it will not stop at the end of Off Peak, if the Soc is low enough). I use the scheduler in TeslaFi to STOP car charging at the end of Off Peak - i.e. it will take me multiple nights to fully replenish if I come home "empty" after a long journey. Others manually set the LIMIT for however much can be charged in one night. So, for example, if that is 40% and you come home at 20% then set the limit to 60% on night one, and then your normal limit e.g. 80% on night two.
The car will use that schedule when at that location (i.e. "Home"). Including if you have a great night out and come home later than the start time
My PowerWall is set up with a Utility Rate Plan. Mine is set for Oct-Feb, because outside of that I rely on my PV as being the primary source, and juggle things for overcast days. I set Time Based from Oct-Feb and Self-Powered the rest of the year.
If my consumption is high (
both cars charging, or something else in the house), the PowerWall will reduce the charge rate (
if memory serves me it is normally 10kW and it drops to 3.5kW - I have 2x PowerWalls in case that makes a difference). So, depending on the length of time for your Off Peak tariff that may not be long enough to replenish your PowerWall if it charges at only 3.5kW for the whole period (particularly for people with an Off Peak period of only 4 hours). But for anyone who doesn't need / use 100% for normal daily usage that's probably fine.
But I'm not sure I'm answering the right question?