Ok, I am guessing that lint built up in the internal vent or the external vent and that is what caused your heating time to increase. This also causes the machine to over heat, and you have thermal safety devices which shut it down (so you do not burn down your house)

You need to open it up, clean it out and check the thermal devices. There is a wiring diagram and tech notes under the console, so get that. Then take out the screws inside the door jam on the top that hold the top on. The top will come off, and this will allow you to take off the front (two screws hold it on, make sure you mark the wires to the door switch and how they go). You can then reach under the drum (if you have small hands, if not get someone who has small hands) and release the belt from the pulley and motor. You can now lift out the drum and clean everything. You will see the thermostats/thermal fuses on the heater housing and on the blower housing.

Test them and replace ones that do not have continuity.

That should do it.