Most of your interviews will be concentrated in December and January.
If you can get an anesthesia elective/sub-I in July/August that is the best time so you can get a letter ... sometimes attendings can take a month or two to get your letter finished. Soemtimes, they can get it done in a week. But, to be safe it is best to get your elective as early as possible in fourth year to get the letter onto ERAS as soon as you can.
Sometimes, it doesn't work out that you can get the elective so early - especially if you have a lot of people in your class going into anesthesia since everyone is wanting to get that early spot. Good luck!