The base time of the timeline index defines the starting point or end point for the timeline.. The base time must be a date-time literal or date-time expression that evaluates to a date and time. The base value is evaluated at the time the load is first initialized by LoadInit, and is never altered.

If defined as the beginning, times that are before the base time are treated according to how the lower bound overflow flag is set.

If defined as the end, times that are after the base time are treated according to how the upper bound overflow flag is set.

Whether the base time is defined as a starting point or ending point is dependant on how the interval is defined for the timeline.