Use LocalDate for session start time calculation

[alv-cor]

Replaced System.currentTimeMillis() with LocalDate.now().atTime(...).atZone(...).toInstant().toEpochMilli() for more accurate session start time based on the routine's scheduled time and system time zone.

[PranavPurwar]

The rest of the app still uses System.currentTimeMillis() for calculation, so changing it just here might cause issues.

[alv-cor]

According to my tests, routines were not working correctly with System.currentTimeMillis(), and it makes sense, since this is not the start time of the routine. I cannot check it since I am using my own version now with this fix, but I encourage you to test it too.