Disable NTP client and NTP server functionality on SRX series devices.
There is actually no way to fully disable the NTP daemon on SRX series devices.
However; you can separately disable the NTP client or server functionality.
For this, all you need is to delete all NTP configuration from SRX so that it doesn't attempt to synchronize with another NTP server.
delete system ntp
If any downstream device attempts to use the SRX as an NTP server, you can configure a firewall filter for the SRX to drop the traffic.
set interfaces lo0 unit 0 family inet filter input NTP-deny
set firewall filter NTP-deny term 1 from protocol udp
set firewall filter NTP-deny term 1 from destination-port 123
set firewall filter NTP-deny term 1 then discard
set firewall filter NTP-deny term default then accept
The filter is applied on the loopback interface to tackle all traffic destined to the routing-engine. The clients will still be able to traverse the SRX to reach an upstream NTP server is needed but the NTP server functionality on the SRX will not work.