You wont learn much between now and the 27th. Unless you sail on a different type of boat everyday 24/7 lol. Its a complex sport/passtime with so many variables that depending on your goals takes many years to master.
Having said all that, classes are the best way. Try to learn on boats similar in size and design to your fantasy boat (assuming your going to buy one) or similar to the boat your chartering (if that is why the rush is on).
The basic skills you will get over the next few weeks will be the gounding for everything else to come and at worst you will be able to make a competant crew for another skipper
. While your doing your classes, see if you can get a ride on a few race
boats out of your local sailing cub. This will help you a lot and give you a feel for a variety of boats.
either way, good luck and fair winds