24 hours real time since your last spin. But there is a glitch where you can spin it infinite times if you want a certain prize. Just need to spin the wheel, wait for it to stop, quit your game completely/turn off internet, and load back in.

There's a 1 in 20 chance of winning the vehicle featured on the podium in GTA Online, but even if you don't win you can still get free cash, clothing items, and bonus RP.