There are two components to the fat grafting process; the liposuction harvesting component, and the micrografting injection component. In general the length of the procedure is dictated by the first part, the liposuction part, as the reinjection part is usually fairly quick and dependant only on how much fat is being injected - usually from about 150 - 400cc.
There is still some discussion as to the best way to harvest and process fat prior to injection. On the one hand there is the very slow process of harvesting using small syringes and centrifuging (spinning the fat), which is considered the gold standard by some in terms of fat survival for grafting purposes. Unfortunately this part of the process is very slow, and can extend a breast augmentation with fat procedure to 6 hours or so. On the other hand there are those who claim that the fat can simply be sucked out with regular liposuction, the fluid decanted, and the fat reinjected. Using this approach, there is likely significantly more tissue loss after grafting, but it is fast and can drop the procedure to under two hours. Generally this approach injects significantly more volume of fat and fluid, with the expectation that much of it will absorb. The one published study that uses a modification of this approach, shows about 65% retention of the original volume of fluid and fat that is injected. This same study also utilizes the BRAVA device to expand the tissues prior to injection to increase the fat retention. As in most things, I think the best answer is somewhere in between, so in my practice, most fat augmentation procedures take 2.5-3.5 hours, using the gentlest harvesting techniques that are practical and using the PureGraft fat purification process, and micrografting injection. The one thing that the patient can do to make a difference is to use the BRAVA. Whatever grafting procedure is used, BRAVA can improve the final outcome by allowing more fat to be injected successfuly at one time.
We are also able to harvest fat extra fat to be stored in our in clinic lipobank so that if repeat procedures for more volume are required, then no further liposuction is required, making the micrografting procedure a 45 minute procedure that can even be done under local anaesthetic.