Are several ways for doing it.
1- as a workflow task
2- as a query ( I sugges webservices for it )
Date is better implemented in version 5.0 than 4.1 but you can solve it without major problems. In 4.1 could be a input and write there the date. If you want to automatize it .. I suggest create simply application with java, using webservices, making the search and sending the mail ( that's the more easiest way to taking it ). In 1-2 days you could get it running. It can be implemented in phytohon or perl too ... it's other possibility. Run a script daily and it's all done.
we've got some push searches ... but you want to change a variable for each day ... and can not be done as "user search" -> try it it's interesting too ... that gives new results of some saved search saved as user search.
