If you have a surgeon that is experienced with performing blocks him/herself, then having them do the block at the beginning of the surgery, is a good option. A former doc of mine was a spine surgeon that became a primary with a focus on pain patients. He did a stellate ganglion block (and had previously done a series of them) at the time of my fourth wrist surgery. His background and skill set was perhaps unusual though...

I found post op recovery pain negligible compared to my regular RSD pain, and with the stellate ganglion block signifigantly decreasing my RSD pain for something like 3 weeks, it made sugery so much less traumatic for me.

All blocks are not created equal. This shouldn't be treated, for example, like an epidural during childbirth, where you receive a small window of pain relief. Do some research on block cocktail options, since this can increase length of results dramatically in my experiene. The experience, skill and patience of the doc are also crucial. With a garden variety diagnostic block, the doc can get their answer without the level of precision you're going to want during this occassion... You should be awake and he/she should use your responses to pinpoint the "sweet spot" for your maximum relief.