It took nearly 16 hours - that's with waiting time and whatnot, not full work - and the mold is finally done.
I managed to pry the back off first. It came out pretty clean too.
The front half was a different matter.
Mu biggest concern was that the mold would be riddled with little air bubbles like the mold for the glove was, and there are some, nothing to be concerned about however. I can probably even patch most of them up once it's all cleaned out.
So now all that's left is to get the silicone - and put in the pour holes, which I forgot to do when I made the mold - and if all goes well, I'll have my first silicone mask and if it holds up, it'll eventually be available for sale online.