It takes just a couple hours. You'll do a little instruction time on safety and equipment, get in the pool and learn how to use the equipment and go out and do a dive. A couple things to note about this is that it does not make you PADI certified...it's only valid for the time you are at the resort so you would have to take the class again if you visit Couples or any other resort that offers diving. Also, only one dive is free...you'll get the class and the one dive free and any additional dives you care to do will be an additional expense.
You may want to consider becoming PADI certified. You can do this in a number of ways. You can do the class entirely through a dive shop at home, there will again be book time and pool time and some skills dives included which they would likely do in a local lake or some such body area uless you live on the coast. Another option is to do the class and pool time at home and do the skills dives in Jamaica...there is a charge for these dives at Couples as it's a completion of your certification not just a scuba dive. You can also do the entire thing at Couples, again for a fee. Our class at home was a two day weekend course plus the skills dives were another 2 day weekend just to give you an idea on time. You can do the book/classroom portion online, do the pool portion through a dive shop and the skills dives either through the dive shop or at Couples. Lot's of options but taking this course gets you a certification that lasts rather than having to retake the class everytime you take a trip. If you are certified the diving at Couples is included...free.
One other thing to note is that regardless of your choice there is a health questionarre you must complete. Any "yes" answers will then require you to have a doctors signature to dive...it doesn't mean you can't dive it just means you need to have your doctor say you are not a danger to yourself or others while participating in this sport. You might want to print it off and fill it out prior to leaving just in case. http://couples.com/images/new/Scuba-...stionnaire.pdf
The resort course needs to be booked as soon as you arrive in order that you get the day you want. You cannot dive within 24 hours of flying either way so bear this in mind when selecting your day. The resort course for a single dive will take a full morning into the early afternoon and this will include your supervised open water dive. This 1st dive will be to a maximum depth of 30 feet and is included free within your holiday package to CTI. After the 1st dive you can take more for a cost of $50 each dive but you will be restricted to the 2nd dive each day again restricted to a maximum depth of 30 foot. If you decided to go for an open water qualification this will take you in the region of 4 days, not full days though and you may be able to do it quicker, the cost can be found via the links in the main website. The dive crew are a great bunch of guys and will look after you ensuring that you are safe and fully enjoy the experience. Go and enjoy.
Regards Dave and Chell