>To expand on Mike's idea, and to increase accuracy, you could start by using a relatively large interval, say 2 Hours, and test the time. As the time gets close to the desired time you can reduce the interval, say to 30 minutes, then 5 minutes, etc to get as accurate as needed. I don't think the overhead would be of concern, this should require very few CPU cycles.

There is no basis for going to this extra effort.