I've been using one dehydrator for about thirty years now, and I have never felt the need for a timer. The standard amount of time for one dehydration session is overnight. If I had a really full load of wet food, then it might require more than 24 hours. Timers are kind of unusual if they handle that much time.
A temperature control is a thermostat. Normally, I just want to crank mine up to the maximum practical temperature, and I don't dry any fragile stuff.
Some dehydrators have an internal temperature sensitive fuse, so if you block off too much of the air flow, the temperature goes up and the fuse opens and must be replaced.