These days it is no longer a madhouse! - the last four years we have been very happy with Sunsail on this point.
We usually step off the boat at 11am and arrive at EIS by 11.45
When you arrive there is a sheet of paper on the chart table for you to fill in with when you would like the taxi to pick you up on your return...and they do seem to stick to this. If you forget (as we did this year) the chap met us as we tied up on the dock and asked us what time we wanted our taxi to leave.
...actually, it all runs very smoothly. This year we (and 20 others) were in an 'Anegada style' open sided - picnic bench - bolted to a pick-up truck - kind of contraption - but we (and our luggage) all survived! We just put it down to the 'island experience'!
Our advice...leave an hour for the transfer and you will end up with loads of time.