Refer below article.

Simple Windows Service that runs periodically and once a day at specific time using C# and VB.Net

Can we set interval time less than 5 second sir.?

Yes you can set in seconds. Use AddSeconds

scheduledTime = DateTime.Now.AddSeconds(intervalSecond);
if (DateTime.Now > scheduledTime)
{
    //If Scheduled Time is passed set Schedule for the next Interval.
    scheduledTime = scheduledTime.AddSeconds(intervalSecond);
}