Limit for 550D in H.264 mode is 4 GByte or 29:59:59. Whatever hits first ...
Try "Movie restart" option. Frames will be lost.
Or go MLV/RAW with all consequences. No fixed time limit there.
@ItsMeLenny: On 650D ExFAT or not makes the difference recording RAW/MLV 720p24 continuously. I tried 90 MByte/s Sandisk (yes, I know 650D's limits) with FAT32 but never passed 1:30.