N+8. It will be easy to calculate the duration of x number of hours and minutes from a particular point in time.
The reason this is impossible on Windows and downright awkward on Unix is because DST changes from time to time. Unless you have something like tzinfo, you cannot work out a particular date and time by merely adding a duration to another date and time in the past.
Instead, you must work out the timezone you are doing the calculation in, then work out whether the duration needs to incorporate a DST change, which involves working out what that DST changeover date and time was...
Of course, it's impossible on Windows because Microsoft only give the start and end datetime offsets for the current year. Amazingly, after all the patches they've had to issue to fix DST changes over the years, they still haven't implemented a Windows equivalent of tzinfo yet. And may never do so, even though they really aught to, given they are one of the leaders in calendaring software.
The reason this is impossible on Windows and downright awkward on Unix is because DST changes from time to time. Unless you have something like tzinfo, you cannot work out a particular date and time by merely adding a duration to another date and time in the past.
Instead, you must work out the timezone you are doing the calculation in, then work out whether the duration needs to incorporate a DST change, which involves working out what that DST changeover date and time was...
Of course, it's impossible on Windows because Microsoft only give the start and end datetime offsets for the current year. Amazingly, after all the patches they've had to issue to fix DST changes over the years, they still haven't implemented a Windows equivalent of tzinfo yet. And may never do so, even though they really aught to, given they are one of the leaders in calendaring software.