To me, that swelling seems pretty big and angry looking, and something that is likely to need vet treatment. It could be an abscess that needs antibiotics, or other type of mass that needs looking into, and possible removal. With rabbits, rarely would the sudden appearance of a significant red and irritated lump, not be some sort of medical issue requiring treatment.
https://rabbit.org/health/skin-diseases/
https://knutsfordvetsurgery.co.uk/should-i-worry-about-lumps-on-my-pet/
https://wabbitwiki.com/wiki/Abscesses
(LINK CONTAINS MEDICAL RELATED PHOTOS)
https://www.medirabbit.com/EN/Skin_diseases/Bacterial/Abscess/skin_abscess.htm
If you won't be able to get to a knowledgeable rabbit vet before tomorrow, it's possible the swelling may subside in a day if it's just something like a bug bite (non life threatening type), and a vet may not be needed. But to me, just from the extreme inflammation present, it looks to likely be something more, that will require medical treatment.
However, if you have cats, or if there is
any possibility your rabbit could have been scratched or bit by a cat, I'd highly urge getting to a rabbit vet immediately, tonight if at all possible if you have an out of hours vet experienced with rabbits. Cat bites/scratches, can very easily and quickly prove to be fatal to rabbits. If in doubt, or especially if your rabbits condition deteriorates, contact a rabbit vet immediately to consult with.
https://www.rabbitsonline.net/threa...bits-please-everyone-read-basils-story.68997/
If you want to list your general location, someone here may have a suggestion for a good rabbit vet if you don't already have one. Or there are some listings in the link below.
https://wabbitwiki.com/wiki/Choosing_a_rabbit_veterinarian
https://wabbitwiki.com/wiki/Category:Canada
https://wabbitwiki.com/wiki/Veterinary_emergencies