The home may have been in Coming Soon status, so realtors know about it and can arrange for immediate showings when it becomes Active. Also, agents can set up custom searches to know instantly when a home comes on the market within the search criteria like within a particular neighborhood. Finally, when a home first appears there is a blank space for days on the market, so 1 Day on the market means the home came on the day prior, so a great offer could be accepted quickly.