About two hours, roughly the same amount of time a card has space for.
You can always modify the skeleton case (the one that ISN'T water resistant to round about 200 feet) and just plug in the charging cable, then you have unlimited time to record, you just need to swap out the cards every few hours or spend the green to get the gigantic ones.
Is there any way to have them record directly to a computer? Through a micro USB or something? With as many guys that have nav computers these days. If it does that. It doesn't take much to throw a slave drive into the computer for bulk storage.