The planets have global positions, but many daily timing calculations are local. Sunrise, sunset, the horizon, and civil time can all change between cities.
This is why a schedule copied from another location can show the wrong boundaries even on the same calendar date.
The local horizon
Latitude and longitude determine which part of the sky is rising and setting. They also influence the length of daylight across seasons.
Ascendant-based rules and house positions therefore require coordinates, not only a time-zone label.
Sunrise-based day divisions
Hora, Rahu Kalam, Yamaganda, Gulika, and several Choghadiya calculations depend on local sunrise and sunset. Their clock times shift through the year.
Near polar regions or on unusual daylight days, a system should disclose how it handles edge cases rather than silently inventing a result.
Travel and current location
For a local day planner, use the place where the activity will happen. For a natal interpretation, retain the birthplace as the chart origin while applying current transits to the relevant location where the method requires it.
Always confirm daylight-saving changes and historic time-zone data for past dates.