Hi LillAnna,
How long it takes depends so much on your age, your physical shape, your endurance, how far you want to walk each day, whether you want to take rest days, how your feet hold out, whether you want to take time to go inside churches and other historic buildings, how often you stop for cafe con leche and how long you sit and visit when you do stop.... I'm sure you get my point.
Many can stride along and easily cover 40 kilometers in a day. Others like to take it easier, explore as they go and cover 20 kilometers a day or even less. If you have not been doing any long walks in preparation for the camino then you may find that even 20 km per day is a bit taxing. It's not that the camino is a hard walk but it does take a certain endurance.
If you have time, why not book 35 or 40 days. That will give you time to walk to Finisterre and even around to Muxia if you are so inclined.
Buen camino
cecelia