Weather-wize there's not a significant difference between February and March.

You'll find more tourists on the island in February vs. March, especially during President's Week but that difference won't be enough to make a major impact on your trip. There'll be another slight influx in tourists during Easter Week (which for 2016 comes at the end of March).

Right now the cruise ship schedule for February 2016 shows 15 ships coming to Tortola, for March there will be 13 so again not too much difference.

Bottom line - go whenever your schedule allows - you won't notice a difference.