Here's the problem with experience.  If you are just starting out, and a situation arises, you tend to do all of the usual troubleshooting and could be there an hour or two getting things to work right.  When you have experience, and the issue is nothing new to you, then you tend to just go for the jugular and are there for 20 minutes.

How should you charge in a situation like that?  I've been doing IT for quite a while now.  There are times when I know the solutions before I arrive based on the customer's vague definition of what is happening.  When you arrive and the fix is a simple click here, click there and a reboot, you are literally there 5 minutes and it took longer for you to get to the location.

I guess that is where the "mimumin charge of 1 hour" rule comes in to play?