I needed, and still need 2 months into HRT, about 3 full days of growth.
I have been using a 5% lidocaine gel applied an hour before the session in a heavy layer, and covered with a strip of plastic wrap on the upper lip, and a larger sheet across the chin to lower lip and up along the jawline. That keeps the gel in better contact and keeps the lidocaine from evaporating away. There are also prescription EMLA creams or pastes that may be more effective. (I haven't gotten a prescription yet.

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Since I'm doing 2 hour sessions weekly, I've also been using a prescription painkiller at very low dosage. (MODS: feel free to cut if I go over the bounds here. I don't think I am, but...). It's a generic version of Vicoden in the lowest dosage. I take half a tablet, and cut that again to two quarter tablets. I take one quarter sublingually a few minutes before starting, and the second quarter sublingually at the one hour point. Sublingual hydrocodone bypasses that first liver pass, like sublingual, patch, or injected estradiol, and has a shorter but stronger pain relief effective period, around 60-80 minutes. (Yes, there are papers on this.)
The drug helps distance me from the zaps, sort of like a rubber band snap on the skin, and makes the session tolerable. It wears off quickly enough that I can drive home shortly after the session ends.
I pack along a little purse-sized insulated bag, which holds a frozen bottle of water and several balloons filled with water (not inflated, just filled, roughly plum-sized) and frozen. These I roll over the areas that have been zapped in the session to reduce redness and swelling.
I'll be happy to answer any other questions on the topic. The electrolyst has been calling me her 'marathon gal'.

I just feel that after being a hairy beast for three days, I want to maximize the crop we get.