Emails are not like phone calls. They are asynchronous.... A bit like posting a letter.
When someone sends an email the timing is not of importance. It is of the understanding of both parties that it is simply a message, with a subject giving a clue as to the nature and importance of the message. The recipient chooses to respond when they see fit. When they open it, read it, respond to it, is their choice. In other words, the impetus is on the recipient to handle and respond appropriately. Which might even mean a bit of organisation and prioritising.
There's no worldwide gang of email gremlins waiting to tell somebody off for not responding to an email within an hour.
Changing the rules on sending emails is like saying "don't post any letters to us between 2pm and 8pm each day". It doesn't make sense. It's immaterial to the way the system works.
Also it makes it a very one sided way of communication. Parents cannot then say "please don't email me after 6pm", right? That is not civilised.... The school is not teaching the parents. They are teaching the children.
Seriously how do some people think? I wonder if they use email at all?
There are things like 'out of office'.... personal reminders... Folders... Colour coding..... "unread email".... "don't send read receipt" etc.....
Emergencies should be handled in a separate procedure. You wouldn't send an email to 999 if it was an emergency ffs.... For that, there is an emergency procedure/ phone number.
Asking someone not to send an email outside of working hours is very strange and gives the impression that this person doesn't understand how emails work. Or worse, that the teacher is incapable of good judgement.
How do you think people email eachother across time zones in normal business?
To whoever says you can't tell when an email is urgent so it should be sent at a certain time .... Seriously I'm going to use an MN phrase now as for the first time it feels appropriate. Are you on glue?! Anything which has to be immediately seen and acted upon isn't suitable for an email if it's out of hours... That's basic common sense.
What is more probable is that one or two parents have not quite grasped the correct use of email. And therefore the school, rather than remind them about the etiquette and give separate emergency procedure so as to prevent further confusion, is unable to resolve it because themselves have no understanding of proper email use.