Once a year is all they need. They can do back to back breedings if they gain weight back.
Example i go by, idk if others do or not.
Say a Female 1700g before breeding lays 900g clutch and is now 800grams after laying her clutch.
If the female say is at 1500grams by the the upcoming season, SHE IS NOT READY, might be weight wise but physically is not, as i like to get them above and beyond their previous seasons weight.
So if she was 1700 last season i prefer them to get back to 1700 to even it back out and gain 1-200 more grams before i will ever do back to back breeding's.
Some people dont care, once they see they hit that 1500g mark they will breed and sometimes strikeout with slugs or nothing.
Learn to read the snake and you can be very successful