Canukgirl,
My wife and I went to Belize for the first time on a cruise ship. We had the same amount of time, 8=5,. We made arrangements on the ship to go to San Pedro, (getting off the cruise ship on a early tender is the problem) as it turned out, because of rough seas and a front moving in , out excursion was canceled. After a heated discussion with the Purser, we boarded a tender...snokel gear in hand...
Upon arriving on shore, not sure what to do,,,
A local young man offered to take us on a snokel trip to corral caye, we stated we wanted to get to San Pedro and Shark-Ray alley...He said we would have to fly...It was what we did...We were taken to Municipal Airport, boarded a flight to San Pedro. Spent the day, snokeled, and had ceviche at Lilly's...Caught the 3:30 (I think) flight back...
So the only thing is getting off an early tender.
Hope it works out..
Be cool, Be careful and God Bless
Dale and Judy