I'd say in my experience, 3 or so weeks after post cycle therapy...But people react differently. Also maybe try taking your clomid for 21 days or so instead of 15. I like to cycle my clomid like this....I find it works more effective for me:
Day one 300mg
day 2-10 100mg
day 11-21 50mg
But like I said people react differently to post cycle therapy. Have to find what works best for you.