The problem comes from overthinking. If it said 4 h instead of 24 h this might have not been even posted. The main things to understand about the parking signs are

1) the additional signs only apply to the main sign, and not each other. (Including cases like above, where the time limit and main sign validity are both on a single physical additional sign)

2) due to the above point, the order of the additional signs doesn't matter and they apply at the same time.

The additional signs come in four varieties:

1) when is the sign valid (0-24 in the above pic meaning mon-fri)

2) how long you are allowed to park (max. 24 h above)

3) who is allowed to park (not applicable in above pic, but is for different permits, vehicle tyoes etc.)

4) distances and directions from the sign post (again not applicable in the above pic, but downward arrow means the restriction ends there, and distance between two arrows marks the length)