Hey Emilio!
Walnut-sized follicles are pretty late-stage, past the best time for the best fertilization rate. Once I feel gobstopper sized follicles, I call the pairing done for the year and focus the males efforts elsewhere. Are you sure you've have no locks? I'd keep plugging away with the same male either way. How long has he been courting them?
Glad to hear you have some animals breeding this year!
-Evan