How long on average does the first lumbar sympathetic block provide relief?

It varies: The block may be ineffective. If effective, the duration of relief can be short-lived or prolonged but usually the former. Repeat blocks are not uncommonly required.

Difficult to say: You can get anywhere from hours to weeks with your first block. I like to see some response. After that I repeat them as needed - as long as I see increasing benefit between injections.

Epidural steroids: Normally the effects are seen within 24-48 hours but can take as long as 1 week. It depends on several factors such as the amount of inflammation, the cause for your never root pain, degree of disc herniation, continuation of activities that may cause the disc to flare up etc. If it does not give you much relief after the initial 2 days, the problem may be whether the drug went to the right place!