Sure the more the better, but i will try to ba e bit pragmatic.
1 full day around the olympia region
2days around the messinia region
2days to discover the whole Mani peninsula (this is the region between messinia and lakonia)
Spend 1 day around the monemvasia region
1 day around the Mycenae region.
As always what it matters is what u want to focus to, history? Landscapes? Old castles? It is one of the most beautiful mainland areas of Greece, with relative very easy access to everywhere by car.
The above plan will give you an excellent overview of thr area.
If it is summer time that you are visiting add 1-2 days to visit Hydra, an island 10 minutes be boat from the mainland. No cars are allowed there, there are plenlty of hiking routes and u get a very nice summer island feeling. about 4 years ago