I saw this answer regarding "early days" in a related question, Meaning of "Early days I know but may help.":
Early days is a British idiom meaning "it’s too soon to make a judgment" about something.
Why, then, do people say "early doors"?
How can a door be early?
"Early doors" in British English has a rather different meaning from "early days" in the linked question. Lexico has
early doors
informal British
Early on, especially in a game or contest.
you should try to wind up their star player early doorsOrigin
Apparently originally with reference to admission to a music hall some time before the start of the performance.
The phrase is also used to refer to customers of a pub who get there right on opening time. There was a British TV sitcom called Early Doors about which Wikipedia says:
Etymology of show's title
The title is a British slang phrase meaning those who arrive earlier than is customary, and was often associated with pub customers who wait for or arrive soon after evening opening, around 5:30 pm. Until the law was changed in 1988, pubs in England closed in the afternoon. Most are now open all day. It is also widely heard in British football circles, and was resuscitated in comments about football. The phrase originates in the practice of British theatres from around 1870 of allowing customers who paid a little extra to enter the theatre early and choose their own seats to beat the rush just before the performance started.
I clearly remember hearing this first from a football (soccer) commentator meaning the same as "early bath" i.e. being sent off the field of play before the end of the game. My guess at the time was that this must be a kind of eggcorn - a conflation of "early bath" and "her indoors" i.e. going home to the wife although I never got to the bottom of it (hence reading this).
Early doors is to leave early BEFORE the doors close. In the pub "Another one? No thanks, early doors, out tomorrow morning" NOT FOR BEING EARLY, as some of the 12 year olds would let you believe.
