If the heat came on for awhile, it could be the coils on the gas valve. Tom ApplianceEducator.com

If you have no heat and have the timer on a automatic cycle, the dryer will run all day and all night. I do not think you have a timer problem at this time. What you need to do is see if the ignitor comes on, if it does, replace the coils. If you want to satisfy yourself on a bad timer, put the timer on time dry on the last 10 minutes, and see if the timer moves. If so, that rules that out. If the ignitor does not come on, then you could have a bad thermal fuse. That is the white piece in the back that is an inch and a half long, by a half inch wide. That part # is you need it is 3392519. You can jump the thermal fuse out if you like. If it works, do not run the dryer that way. That thermal fuse is the only thing in the way of a dryer burning down the house. If the thermal fuse is not the problem and the ignitor still does not come on, that leaves the flame sensor, which is mounted on the side of the flame tube, and the ignitor. If you have an ohm meter, you can pull the 2 wires off the flame sensor, and check for continuity. Let me know what you find. Tom ApplianceEducator.com