The message has already been saved, so there's no user interaction at all. Since it makes sense to let users choose the interval, a front-end can be written to talk with the program (ie. stop it, then start it again with a new interval), or a simple configuration file can be used. This is perfectly suited to a daemon (or service if you like Windows lingo). In fact, if you didn't write it as one, I would question the quality of your design.
I want to write a program that checks for the time(date) and when it reaches
the specified date, it sends an email (written and stored before) directly