24 Hour Stamp Set Sale! Mark Your Calendar! October 21, 2019November 7, 2019 ~ StampKnowHow ~ Leave a comment Visit StampKnowHow.com on October 23 for the flash SALE day! For 24-HOURS ONLY, you can save 15% on select stamp sets. This sale will be over at midnight, so mark your calendar so you don't miss out on the savings!