I read in a study that in the first 10 seconds, about 95% of the cannabinoids are absorbed.
I timed my most frequent type of hit, either with water or dry, i tend to take a +30sec hit, can go as long as 45sec, and then i hold for 5 sec, and i exhale slowly for about 2-3 seconds, inhale again and then i exhale the rest.
I do like to see the vapour, it is a pleasurable thing to me.. sometimes i even make rings like when i used to smoke. And i don't have the patience to do small hits and seeing no vapour at all most of the times, although sometimes i do the exhale for 2sec, and the moment i see the vapour i hold it for 10sec and usually there is no more vapour in the second exhale. This is not the norm though since i seem to not notice that big difference between the two methods i use.
I think the important thing to keep in mind is to do a deep inhale. I use a respiratory technique i learned in yoga, where you inhale by inflating your belly first, then you open your rib cage and only then you do that inhale where your chest goes up.
I find this helps me maximize air volume and absorption, as well as a longer inhale time.
If you do a shallow breathing and quickly exhale, that is when you are wasting cannabinoids. If you do a long inhale, you are absorbing the cannabinoids already in your lungs and at the same time you keep filling up more.
BUT, and this is only an hypothesis, if you do a 15sec DEEP inhale, and then inhale just air, and hold it in for 10sec for example, that would be one of the most efficient ways to inhale.
When i do it this way, i almost never exhale any visible vapour.