The Start Date is the first date the coupon can be redeemed. The End Date is the last date the coupon can be redeemed. For example, I create the $5 off coupon with a start date of today and an end date of today. Customers can subscribe to the coupon all day today but will not be able to subscribe to it tomorrow.
I set up a monthly $10 plan and a $5 off coupon. The $5 off coupon has the following details:
Max Redemptions = 3
Duration in Months = 6
Start Date = Jan 1, 2017
End Date = Today
Coupon has been redeemed 2 times.
Joe Simple wants to be on the monthly $10 plan and has the $5 off coupon. Joe can apply the coupon. Today is before the End Date and prior to Joe applying the coupon we had not yet reached the Max Redemptions. The result is the max redemption count will go up by 1 to its limit of 3, and no other customer will be able to apply this coupon. Since the duration in months is set at 6, Joe will receive the benefit of this coupon for this month and the next 5 months, or Joe will receive $5 off for the first 6 months. (Note: Duration in Months does not increase the redemption count.)