When older deficient folks take hGH, it take around 6 weeks to really feel the benefits. Someone in this group facing surgery and wanting to optimize healing would want to get on hGH well ahead of the surgery.
For someone 25 years old, your baseline GH levels will be very good and things are working quite well already. So while the increased metabolic response will be comparably less, you should get it on board somewhat in advance.
If you are producing 1 IU now, the benefit of the first IU that you will take will be zero as you shutdown your own production. So taking small amounts serves no purpose. 2 IU make get you to IGF-1=300+ which is very good.
With an healing process, there is a lot of inflammation and a series of different growth factors that really get the job done. GH will simply support that process. I have seen a 70 YO woman with a total knee replacement who healed and progressed extremely well. Many do not and dedication to rehab is critical. But in that 70 YO case, you can also assume that HG levels were quite low. So GH is not the only factor. Rehab supports range of motion and circulation. Over all metabolic rate is also important and I could insert my standard rants on thyroid function, iodine, Vit-D3 etc.
Some serum testing of UG GH seems to indicate that it is as good as pharma [reported to me].