The period event is only available as a planned environment. Define period events to be contiguous, as follows:
- Daytime: 8:00 a.m. to 5:00 p.m.
- Nighttime: 5:00 p.m. to 12:00 a.m.
- Daytime: 8:00 a.m. to 4:59 p.m.
- Nighttime: 5:00 p.m. to 11:50 p.m.
In the latter case, at 4:59 p.m., TASM would change the state to something not associated with Daytime or Nighttime (perhaps the default Always). Then at 5:00 p.m., the state would change again to the one associated with Nighttime.