germany
There are no special "school zones" whose rules one would need to know. Schools have normal traffic signs, maybe with an explanatory text attached:

This says in order
- "Speed Limit 30 km/h"
- "School"
- "Next 300 meters"
- "Monday to Friday 8-16h"
It would have the exact same meaning, if someone removed the "Schule" part.
So the question is, what happens if that information allows you to make an educated guess that today would be an exception? For example, what about Good Friday, a public holiday inside the Easter school break with no school for a week before or after anywhere in the country?
Well, it depends.
At least one court ruled that it is not up the individuals to grant themselves exceptions. If there are exceptions, for example public holidays or school breaks, the authority that placed the sign should include them. Otherwise, the sign overrules personal opinion on whether it makes sense, a sign is a sign and needs to be followed.
OLG Brandenburg, Beschluss vom 12.9.2019, Az.: (2 Z) 53 Ss-OWi 488/19 (1774/19)
And on the other end we have the opposite ruling, saying that public holidays, in other laws and regulations commonly treated as Sundays, do not fall into the range of a sign saying "School, Monday-Saturday".
Amtsgericht Wuppertal, Urteil vom 28.1.2014 (Az.: 12 OWi-723 Js 1323/13-224/13)
So.. yeah... it depends. I am pretty sure that both cases cost the defendant way more time and money to fight then they could save in their whole life slightly speeding in a 30 zone.
Maybe not speeding is the best way to save time.
Legally... it's a crystal clear "uh... maybe? "