I'd say you will have plenty of time, depending on your mode of transportation.

Cab from Logan to Hilton is about 25 minutes and ~$25. Subway (T) is about 30-40 minutes and involves one transfer (blue to green line).

Cab from Hilton to Harvard Square is <10 minutes. T from Hilton is about 20 minutes b/c you have to transfer from green to transfer to red line. A slightly quicker way is to get on the #1 bus (in front of Tower Records) which goes straight down Mass ave, across the rive, and into Cambridge. #1 bus' last stop is Harvard Square.