32g SD will last about 6 hours. 64g all day and then some. I use SanDisk Ultra SD cards as they are waterproof for 7 hours submerged, supposedly, I've never tested that.
I carry spare batteries and have a add on battery pack as well. With the two batteries I have about 4 hours to record. The standard batteries issued are 1100 mA, but you can get 1400 mA ones online fairly cheap. Gives you a little more time before you have to change them out. Add the spares and I can go all day. I keep the spare batteries in a waterproof case under my seat (PA) and it is easy to change them out, just don't get water inside of the camera.
I generally don't want to miss the initial hookup so I just run it constantly. Sometimes the initial hookup is about all I get,
To counter watching endless videos files, I stop the camera every so often and restart it. The creates a new series of files on the SD card. The camera usually separates the files into one hour (+/-) segments using a number sequence, the first files in the series will have a name like GOPRO0071, the next in the sequence is GP010071, then GP020071 and so forth. When you stop the camera it will assign a new number to the next series of files, like GOPRO0072 in this case. I try to keep track of how many times I turn the camera off/on so that if there is something I want to use I can get real close to the right file without going through 6-10 hours of video.
Hope this helps.