I have a windows service handles events triggered by a System.Timers.Timer. I want to set the interval of that timer to 3 months.
The Interval property of the System.Timers.Timer is an Int32 in millseconds, and Int32.MaxValue is smaller than 3 months in milliseconds.
What should I do?
You would re-think your design. Store the next time you want to execute your event (e.g. registry, file, database, ...) and then wake up periodically to check whether that time has passed. Even if you could set a System.Timers.Timer for 3 months, the system would likely reboot before the timer went off and you'd lose your event.
Another option would be to use a scheduled job executed by the Windows Scheduler. It would run a small program that sends your service a message saying that the event has occurred. This would be less resource intensive - though more complex - than waking up periodically to check whether the 3 months had elapsed.