Hi J,
The following two function might help:
StandardWeek.TimeUntilNextValue(TimeNow) - the amount of time before a change in Schedule
StandardWeek.TimeOfNextValue(TimeNow) - the duration of the next value in schedule
StandardWeek.NextValue(TimeNow) - the next value in the schedule
So create a schedule and reference the schedule in your expression builder.
Regards,
Willem