the time limit is imposed by ordinary cameras because they use a random access file structure. the largest any file can be is 2 GB. camcorders work differently, they also make 2 GB files but they are sequential files, so there is no fixed recording length other than the size of the media (ie SD card). dSLR are peculiar in that they also have the heat problem, but all camcorders are designed for continuous use so that won't be an issue with them. the battery supplied with camcorder normally are good for 60 to 90 minutes of recording time per charge. you might either get a larger battery or use an AC power supply for 2 hours. also if you are using other battery accessories, like wireless mic, you need to consider their battery run time limits as well.
before the "big day", do a dry run test of all your equipment to insure that it will run as expected, thus hopefully avoiding any problems.