Another approach is to Just Not Schedule Anything In The 02:00 To 03:00 Time Slot

Actually, that wasn't the OPs problem. (And it's not everywhere in Europe that clocks move at 02:00 - Europe moves at 01:00 UTC, which is 02:00 local time in large parts of Europe, but 01:00 local time in the UK, Ireland, and Portugal, and 03:00 local time further East). In fact, if he had done the calculations based from a 02:00 timestamp, he wouldn't not have run into problems. Assuming a DST shift of one hour, the OP could do his calculation of taking the date of the time 24 hours earlier if the time component is between 01:00:00 and 22:59:59.