You can't "write a program to run at a specific time" - it's either running at the time, or it isn't. You can tell you operating system to run it at a specific time and (assuming the computer is powered on and working) it will do it.
For Windows, you would use the Task Scheduler:
Task Scheduler (Windows)[
^]
The other approach is to run the app when the computer starts via Startup, and have it check every sixty seconds or so if it is time to do something.
Either way, you need to write the code to send your emails, and tell the operating system when to run it. This may help with the email part:
Sending an Email in C# with or without attachments: generic routine.[
^]
Submit an article or tip