I think I understand the OP's intent so I will answer. By shortening the checkouts to one day would that lure more people into the sport? Having people only burn one day would save on their time, money for food and lodging where ever they travel. Allow them more diving if the cert is just part of their vacation. If the spouse they travel with say you can have one day and the rest of the vacation is mine. Ect ect. I'm sure there are as many more reasons I can't think of.
The negatives have to do with stress loading on the students caused by a shorter SI between dives (not having overnight to think about it).
The one new diver I have brought this up to said she wished her OW was one day so that she could have gotten on to diving the rest of her vacation. She didn't think there would be any problem with having a shorter SI, hours instead of over night. FWIW.
Correct...
I would say that approximately 1 out of every 2 students I certify ask if they can complete everything in one day (when told they have to do it over two.)
I don't want to seem like I'm tooting my own horn, but I believe this is because they feel so good about their skill level after pool work that they don't understand the need to drag things out. I agree with them - assuming... and let me be very clear... that when I get them out for checkouts... dive one and two go off without a hitch... buoyancy is pinpoint - skills are as fluid as they were in the pool etc... and we move on to dive three with the same results... it makes absolutely no sense to have to come back another day for one more dive.
It is not unusual for this scenario to play out. We arrive at the local quarry at 8:30 and are in the water for the first dive by 9:15. We get out at 10:00 after a nice 45 minute dive. We do a 45 minute surface interval and are back in the water at 10:45. We complete a second dive of 45 minutes and are out of the water at 11:30... we take a one hour surface interval - lunch break and are back in the water at 12:30 for our third and now final dive of the day... we are done at 1:15 after another 45 minute dive.
Nothing is rushed and the dives are very thorough... I'm regularly asked why we can't do the final dive and be done. My students are ready. They feel ready and I know they're ready. I also know this is exactly what they'll do when they get to their vacation in Bonaire or on that live-aboard. If we took another one hour surface interval and got back in the water at 2:15... we'd be done our 4th and final dive at 3:00pm... finish up all the paperwork and be on our way home.
The arguments I've heard against this here are weak. We need to give the divers time to collect their thoughts and ask questions? Really? I think if divers have that many questions at checkouts, there is a good possibility their training course was lacking.
I am happy to answer questions before, during and after the process... but I've never in my 8+ years of teaching had a student come back and ask a question on the second day that they didn't ask on the first as the event causing the question occurred. The only question I get is "Why did we have to come back for a second day for this - we could have done this 4th dive yesterday."