As the developer answered my question here , you can simply use the date instead of the day (s).
BackgroundJob.Schedule( () => Console.WriteLine("Reliable!"), new DateTime(2015, 08, 05, 12, 00, 00));
For 08/05/2015 at 00:00.
Jerry's answer is correct for RecurringJobs
RecurringJob.Schedule( () => Console.WriteLine("Reliable!"), "00 00 05 8 *");
which will be launched every year 05/08 at 00:00
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