I don't do software for Windows or AHP, but for my own edification could you kindly provide more details as to what you are looking for and how you would expect to use it.
For example, would you expect your Sabbath and Holy Days to begin at sunset computed for your own locality or for Jerusalem, or expect it to begin on some astronomical announcement? Would you accept US Naval Observatory computations for sunset, and how close to their computation would be considered sufficiently accurate for your use.
I assume you would expect to be mixing timers based on the Jewish calendar with timers based on the Gregorian calendar in the same schedule. Is that correct?
To take a different tack entirely, would it be acceptable or better for your purposes to have the Sabbaths and Holy Days defined by their (variable) dates beginning at time 00:00 in the Gregorian calendar, but understood not to officially begin until sunset on those dates? Considering that with days measured between sunsets that some days will be longer and some shorter than 24 hours, and years can vary in length, can you provide a few _extreme_ example of how you would hope to be able to program timers. For example, if I were planning to attend a (western) New Year party and wanted an X10 alert exactly one hour before the official New Year in my locality, I would program 23:00 on 31 December. But if I wanted to be alerted exactly one hour before Rosh Hashana, programming 23:00 on 29 Elul would be somewhat different than one hour before sunset and therefore technically incorrect.
A lot of the above may seem like nitpicking, but that's what it takes to write software.