What does it mean when a school zone sign indicates a speed limit of 30 km/h?

• You must slow down to the indicated speed between 8 a.m. to 9 a.m. and from 3 p.m. to 5 p.m.
• You must slow down to the indicated speed during hazardous conditions
• You must slow down to the indicated speed between 8 a.m. and 5 p.m. on school days
  Explanation:

  "You must slow down to the indicated speed between 8 a.m. and 5 p.m. on school days"
• You must slow down to the indicated speed at all times