How long can I wait for a second FUE procedure?

A follow up hair transplant immediate after your surgery should not be scheduled based on your doctors "opening" or availability.  In general we inform patients they need to wait until the hairs grow out before considering another surgery.  You don't want to overlap transplanted hairs.  The only exception is if you want the transplant on a different (virgin) area of scalp.

To
see full results of a hair transplant procedure, it typically takes about 12-15
months.  We recommend waiting at least
that full year before planning your next procedure, so you can see exactly
where you may or may not need more work!

If the donor site and recipient site has not been used in the previous operation,it is possible to perform the second surgery anytime.On the other hand if the donor area is used homogeneously in the first surgery and for the second surgery the extraction will be done among the first extraction area then you should wait approximately 6 months.Secondly if the recipient area is the same area then you have to wait at least 1 year for increasing the density with a second surgery.If the recipient area is apart from the first surgery recipient area then anytime you can have the second surgery.

If you are implanting in the same area, you need to wait until your hair grows in so you do not implant into the transplanted hair.  If it is a different area, with FUT I would wait until the donor area is loose and there is no tension so about a year and with FUE about six months. 

Generally I wait for 7-8 months to see the result of what I did in the first procedure. In this way I can add hair to any specific areas that may need more density. If you doctor wants to do it 20 days later, he should stay away from the recipient area where the initial grafts were placed as this area still has healing to be done. If the first transplant was in the frontal area and the second will be done in the crown, then 20 days spacing may work out if the FUE area where the grafts were taken from is completely healed.