How would i get the time elapsed since the plr last joined? I don't need a script, just a service or something that would be needed to do so.
I would store the data derived from the functions here and store in datastore the Player's visit each time they leave the game .. when they arrive, you can do some math to figure out the days, or simply post their last visit date..
This should give you a head start:
https://scriptinghelpers.org/questions/25121/how-do-you-get-the-date-and-time-from-unix-epoch-time