Thanks for bringing this topic up.
Good review:
We did not observe a significant decrease in sperm concentrations despite marked suppression of T and gonadotropin production with DMAU administration. However, this was not unexpected given the length of treatment of 28 days, the 72 days required for the completion of spermatogenesis in men, and that maximal suppression of T production was not observed until day 7 of treatment. Interestingly, 4 of 59 men in the treatment groups did achieve sperm concentrations of <5 million/mL at 28 days, whereas none did in the placebo group. The effectiveness of DMAU in suppression of spermatogenesis is currently being studied in a longer-term study. In studies of injectable androgen plus progestin combinations ([33](javascript:;)), sperm concentrations begin to fall after 4 weeks of treatment, but require at least 6 to 8 weeks to demonstrate marked suppression of spermatogenesis to levels compatible with contraceptive efficacy.
Look at reference 33:
You’d have to be a riverboat gambler to try and time fertility using a hormonal contraceptive method with a male. If you superimpose a women’s fertility using the pill the onset of action (~99% effectiveness) is ~ 10x faster and works within a week if you do it correctly.