I don't know if this is mentioned somewhere, and if so I'm sorry, but is there a force join option for ladder games, or does having automatic boot turned on force players to automatically join a game once the autoboot timer is reached?

I'm curious, because I could foresee people stalling games simply by choosing not to join a game for an extended period of time.

it should be the same as the direct boot timer for those games, which is 3 days

Yes, the Force Join system works the same way for ladder games as it does for tournaments. The auto-boot time will also mean that nobody needs to click the Force Join button, they will get joined automatically after 72 hours.