One of the things you need to consider when hiring a magician is what show you should go with. The main factor to consider is venue and number of people. For the walk around magic (where I travel group to group and perform for 5-10 minutes per) it is generally booked by the hour and is ideal for a reception before a dinner where you have 50+ guests.
For, say, house parties or groups of less than 30 you should consider a show for the entire group at once. This show is a little customizable and runs between 45-60 minutes.
What about groups between 30-50 people you ask? I'm happy to discuss options, but you really can go with either of the above!