My Fiancé Quit Smoking 19 Weeks Ago (a Week Shy

My fiancé quit smoking 19 weeks ago (a week shy of 5 months ago) on February 5th 2018 after smoking for almost 20 years. He'll be 35yrs in October 2018. I quit smoking 4 years ago and had smoked about 7 years. I just turned 32 in April 2018.

My question is how long should it take for his sperm to reach optimal health to be able to successfully and healthily conceive? We began our 4th try (trying to conceive) when he had reached 18 weeks (126 days) of no smoking.

Thank you for your help.