There are lots of different opinions on this. But if you go to the web site of the Urologist in Chicago who pretty much discovered the the use of the PSA test in the 1990's, you will find that he suggests using ED drugs immediately after surgery.
My urologist waited until the catheter was out at two weeks post open surgery and then had me start on Viagra with a daily dose. I was on ED drugs prior to the surgery due to hypertension and had saved up pills. Once I found this web site and ADC, I switched to getting the drugs from ADC.
The ED drugs didn't help that much, so at 3 months I started using a VED. Then at 6 months, I went to Injections.
I would not wait very long, just my own personal opinion....