Like you, I tend to be a stickler for spelling and grammar that I learned while growing up. The use of the spelling
alright still chafes, since I think it started as a misspelling similar to the correctly spelled
already. But over the years, it has become officially accepted spelling by mainstream dictionaries. The same can be said about
till and
'til -- if you look up the former on any major dictionary (like
Merriam-Webster or
Cambridge) it will say that one of the definitions is as a synonym for the latter. It's unfortunately something we spelling/grammar buffs have to accept with the changing times.
I looked through the Gboard settings, and unfortunately don't see any way to set up a personal voice dictionary to spell certain words in a preferred way. Perhaps the best approach here is to use the full word
until when dictating, rather than
'til.