I wanted to start a Windows service to run a function everyday at specific time.
What method i should consider to implement this? Timer or using threads?
Use Windows built in Task Scheduler (http://windows.microsoft.com/en-us/windows7/schedule-a-task) or Quartz.net.
Unless ... you have a service that's doing lots of other processing and needs to be running all the time in which case a Timer might be appropriate.