I would think you could easily combine Egypt and Greece into one year. You should be able to cover Egypt in 12 weeks or fewer (depending on the age of your children and which resources you include). Then the Greece study is done only one day per week in the original handbook, so you should have no problem.
if I may make a suggestion: Be sure to keep a Book of Centuries, so your children can see how the civilizations overlap. I find it fascinating to see how Sparta was being founded at the same time as Moses and the Israelites were wandering in the wilderness. Those ah-ha moments are priceless.