I’m confused if your reviewer are receiving the reminders too early (“receive the reminders early with respect to the due date”), or too late (“sent to reviewers after the due date”).
I will note however, that in OJS 2.4.6 there was great ambiguity with regard to the reminder to accept or decline a review invitation vs. the reminder to complete an accepted review. (The same message was used for both communications!) See:
This was resolved in 2.4.8, and may relate to your experience.