Creating a flag based on date and other criteria that is carried throughout

Hello,

So I'm trying to create a flag/indicator that once the flag is initiated, it's carried throughout a certain period of time.

For example, if you came to a store and spent $50, for the next two weeks you'd get a 25% coupon applied to your cart. But after that, the coupon goes away. But it's specific to a person. So I feel like an LOD could be applied somewhere but I'm still learning and just want a direction to help get me started. If anyone has any advice, that'd be appreciated!

Name               Date     Total(before coupon)          coupon(flag)   new total

Dave               5/1/19     $40                                   no                    $40

Dave               5/5/19     $55                                   yes                  $41.25

Dave               5/7/19     $30                                   yes                  $22.5

Dave               5/30/19   $20                                   no                    $20