It kind of depends on what the spots are. If it's accumulated powder that didn't fully dissolve in the dye water, you might be able to wash it off and have minimal staining. If it's points that accumulated due to contact of the visor to the dye pot, your hangar or something else it may be a little bit harder.
Dye in general won't be able to be scrubbed off easily so you might have to re-do the visor. Depending on the severity of colour inconsistencies though you might be able to get away with having a few spots though since there won't be light coming from the inside of your helmet which will help limit differences in the shade of black since it'll be dark inside the bucket. It's definitely worth doing a dry fit before scrapping anything.
I had it boiling for 45 minutes, but from the looks of it, I have no choice but to do it again. However, I'm down to my last pack so I will have to adjust the water in accordance to the packet because...
It looks like an oil painting at this point. Alright, I hope I can get it right this time. So this time around should I just keep dipping it instead of dipping it once?