This no longer appears to be the case. I haven't configured anything special but when my phones request NTP from their default gateway, which is a Meraki MX, the MX responds as seen in the following capture.
I'd open a case with Cisco Meraki to ask for a switch to disable it or to configure. You can't. It's in the DHCP Options. You have to overwrite it with your own DHCP NTP / Time Server Option.
We are establishing our own DHCP Server now, like we did with VPN and IPv6 Router...
Meraki was a mistake.
Whilst you can't set up an actual NTP server, there are a couple of DHCP options which may allow you to achieve what you need -
Option 4 (Time Server)
This option is used to specify the time server available to the client. This is also related to the Time zone offset option.
Option 42 NTP servers
This option carries the NTP servers used on the network.
See - Setting Custom DHCP Options these work for both switches and security appliances.
@Asher is there a real requirement for a local NTP server, can you not rely on an external NTP like time.google.com
Otherwise does your router not include an NTP option?