It probably depends on what you are interested in, and what time of year you are going.

As of this time, it is very hot to spend lots of time walking around temples, but the beach scene about 15 minute walk from Kamakura is rather interesting, so I could envision a schedule of one day checking out the beach life in Kamakura/Enoshima, crashing at a cheap place (Hotel New Kamakura is not without its charm), and then getting an early start on the temples while it is still slightly cooler the following morning.

Outside of summer, I'd say that a day trip should be sufficient unless you really like old temples and hiking, in which case I'd still recommend the forementioned place for a one night stay.