How to get a list of dates when the time changes to daylight savings time and back for a specific timezone?

Question

JavaScript

Good afternoon!

How to get a list of dates when TimeZoneOffset changes depending on a specific time zone.
It is necessary to count a lot of durations of events, taking into account the calendar of working hours.
If you count with the help of libraries, it turns out very slowly. A simple algorithm works 300 times faster, but there is a problem with DST time. And I need to somehow quickly determine how many and with what offsets of switching between timestamp Start and timesatam End