Hello, XXXXXXXXXXX
Cats can go into estrus any where between every 3-7 weeks. The estrus cycle can last any where from 7-21 days at a time if ovulation is not accomplished. Cats are induces ovulators which means they need to have intercourse to ovulate.
Let me know if you need more help.
Sincerely, XXXXX
Expert in cat behavior and health
Expert in cat medical and behavior issues.