An Hour seems long. I'd go with what 'meself' says above.
Looking at my old book seems like 8 or 10 for each set, set being 40 or 45 mins.
For a short while I did 'Pick your own set'. Dished out list of 100 songs and tried to do what was asked. Very Difficult keeping track and singing as well. Best night was when someone volunteered to do the collation. Enjoyable and saved a lot of planning but I often had to do songs not requested to try and maintain balance. Bad idea.