According to USA Today, the best time for whale watching in Massachusetts is from April to October.

We got seats at the bar as well, but we wanted seats in one of the rooms so we could sit by a window. To get a table in one of the two rooms $50 needed to be spent, and we were already stuffed from dinner so apps and desserts were out, and we had 2 bottles of wine at said dinner on top of all the pre-dinner dranks...so trying to force $50 worth of drinks just didn't seem worth it at that point. There's no minimum that needs to be met at the bar though, just don't get the primo views.