Use the Timer Tick event to check (check the appropriate box), and then in the tick event:
DateTime Now = DateTime.Now;
if(Now.Hours == DateTimeCallX.Hours
&& Now.Minutes == DateTimeCallX.Minutes
&& xHasRan == false)
{
x();
xHasRan = true;
}
DateTimeCallX - A DateTime object set at 20:00.
xHasRan is a logical expression indicating whether this function was called, it will initially be set to false and will be set to true after x is called, so if the timer timer starts again at that minute, it will not run this function again.