Ri?

[Bogertophis]

How long can this take to become lethal. Im gonna try and bring him to the vet tomorrow.

Not a big rush, as long as his mouth isn't bubbling or full of mucus...because snakes cannot cough, they can choke to death with an RI. Usually an RI takes at least a few days to get going, but hard to say...just like people, some snakes have better resistance than others. Not so sure this even IS an RI, snakes can
have a little cage debris, a bit of shed skin or water in their nostrils that can make a little noise & still be harmless. Yawning doesn't exactly indicate an RI.

Have you lowered the heat on his warm side? That's an immediate need.