Configuring offers with start / end times allows you to preconfigure and setup offers for the future. This makes scheduling flash sales or coordinating offers with marketing easy. The dates / times you choose are all shown to you in local time.

If you have set up an offer and want to show it only to a specific set of tagged customers, you can create this filter easily. This can be used to give different offers to different sets of customers. This can be configured under the optional setting when editing your offer.