It depends if you start it up with switches or with the short cut key. The switches could take you a little bit, the short cut key takes a couple minutes on a big jet.
Start and shutting down are easy, what is hard (and fun) is knowing what the heck ATC is talking about, reading charts properly, getting charts in advance, planning the flight, having a perfect landing.
Alright so some of those things aren't fun by most people, but call me lame; I love them.