We're keeping it brief as we'll do a full article on this soon.
Most cameras will go to around 30 seconds for the longest shutter speed possible, and sometimes it isn't enough. Switching the shutter option to bulb mode will allow the shutter to stay open for as long as the button is depressed.
5 minute light trails? No problem in bulb mode. We'd suggest using a remote shutter cable with a lock on though.