I have been using Mitchell for nearly 8 years. Do you have Manager Plus?
If you use the Part/Labor guide the labor time is transferred over to the estimate. You can also build "can jobs" for those jobs used on a daily basis. For example, Tire Rotation, Wheel Alignment, LOF, etc. For those jobs you can set up a generic labor time. You can also create vehicle specific can jobs. For example, if you do a lot of work on Honda Vehicles, you can set up a Honda Rear diff service can job, with the parts and labor already set. This is where the program is powerful because it lets you tailor the program to your needs.
You can also add the labor times as you need if the job you are doing is unique. For example; removing a hitch for a customer. This job is not found in the Parts/Labor guide and something you would not make a can job for. For this, you simple hit the labor tab and add the labor time as needed.
The Mitchell system has a lot of help screens and video, I recommend going thru them. Also, ask your rep for help.