When you do it that way, {today} in the subject line works. If you're only getting one result from the saved search, then that doesn't matter and it will work fine. I will say that {today} was formatted YYYY-MM-DD, and if you want to change the format, you can use formula's. For instance,

<%=TO_CHAR({today},'MM/DD/YYYY')%>

works for me, when Summarize Scheduled Emails is unchecked.