Timeframe rules allow you yo limit when a voucher will be valid. They are similar to the time of order rules but instead of they of weeks this rule defines a start and end date when a campaign is active.
A perfect use for this rule would be a sales event like new year sale. By setting timeframe rule from 1st January 2019 to 14th January 2019 you will make sure that only customers ordering in the first two weeks of 2019 will be able to use a voucher.
If you set multiple timeframe rules only one of them has to be valid.