Some people have said it respawns after a week or 10 days in game, but I never had it respawn and haven't seen it confirmed that it does respawn. I actually wasn't even able to get money off it it originally.
Your best bet is probably just going through the story and doing the heists, then do the assassination missions afterwards. I haven't gotten all the way through myself, but there's no real reason you need Franklin to have a lot of money before then anyways. I was the same with Franklin and still bought the weed store and the cab company, anything after that is just futzing around with upgrading cars and stuff.