Time Zones and Daylight Saving Time

GDBM XI works with Daylight Saving Time and all time zones when scheduling and running entries, such as reconcile and post.

When a user creates a new scheduled entry in GDBM XI, the user’s local time zone is permanently assigned to the entry. GDBM XI uses the time zone from the local machine’s operating system to determine the time zone that should be assigned to the entry. This becomes the reference time zone associated to the StartTime and StopTime for each scheduled entry.

When a user outside of the reference time zone views a scheduled entry, the time displayed is automatically translated to their local time zone according to the time zone set in their operating system. For example, a StartTime of Wednesday 11pm in Mountain time zone is displayed with a StartTime of Thursday 1am for a user in the Eastern time zone.

GDBM XI uses the offset from Coordinated Universal Time (UTC) to translate the reference time zone to the viewer's local time zone at the moment they view the scheduled entry. It also factors in whether each participating time zone observes Daylight Saving Time. This means if a user views a scheduled entry just after Daylight Saving has transitioned in their time zone, but before it has transitioned in the reference time zone, it shows the appropriate time difference at that given point in time. For example, if a viewer in the Eastern time zone views a scheduled entry with a reference time zone in the Mountain time zone after the Daylight Saving transition has occurred for the Eastern time zone, but before it has transitioned in the Mountain time zone, instead of the usual two-hour time difference, the user sees a difference of one or three hours for the scheduled entry, depending on the time of year.

Event Start Times Occurring During Daylight Saving Time Transitions

1. Ambiguous StartTime: What happens on the day of a transition from Daylight Saving Time (DST) to Standard Time (the autumn transition when we “fall back” an hour) when the scheduled entry StartTime is 1:30am?

   This value is ambiguous since it occurs twice on the same day during the transition from DST to Standard Time. When the clock reaches 2am, it jumps back to 1am and runs forward, again revisiting all moments from 1am to 2am for a second time in the same day. 

   To resolve an ambiguous StartTime, the GDBM XI processor uses the earlier of the two possible occurrences of the given time.

2. Invalid StartTime: What happens on the day of a transition from Standard Time to DST (the spring transition when we "spring ahead" an hour) when the StartTime is 2:30am?

   That time value is invalid on that day since the clock jumps to 3am the moment it reaches 2am, skipping over all moments in the interval from 2am to 3am.

   To resolve an invalid StartTime, the GDBM XI process subtracts one hour for the scheduled start time, so the scheduled entry begins an hour earlier than usual. For the example above, the entry would start at 1:30am rather than 2:30am.