Random thought about petrification and the current situation:
Chrome, Kinro, Nikki and possibly other unseen characters held hands to form a chain, so I guess either they are expecting to be depetrified in a single go with the reverse chain reaction or they wanted to show Senku the chain reaction travelling through them to help him connect the dots. The second thing could only happen if the chain reaction moves faster than the beam. Also Chrome left his arm pointing up and there's the posibility of him holding an objec in that hand, so there's the posiblity of something something lighning -> reverting back. Senku got revived by depleting an unknown element in his stone body + nitric acid, but it took him 3700 years and that something should be refilled if he's turned back to stone. Burning himnelf with nitric acid in anticipation shouldn't work (he's supposed to be out of nital).
I don't know how knowing that the speed was constant helps, or how it fit the original beam. The original beam seemed to travel along the earth's surface at an extremely fast constant speed instead of growing radially at a constant speed. If it had been radial, then it would have covered the ISS and also from Japan's perspective it would have suddenly appeared from under the floor instead of getting a glimpse from the horizon before getting hit.
Senku originaly thought of nital because it was related to nitric acid and mentioned something about it acting over the carbon bonds before Taiju interrupting him. He never tried any other etching agent that could work on a similar principle.