I tried this rule: /ip firewall nat
add action=src-nat chain=srcnat out-interface-list=WAN protocol=udp src-port=123 to-ports=12300
with a Tweak instead of Out-interface-list, I used “Out Interface” and specified the WAN interface. Turned OFF the NTP client and re-enabled it and also It did not work 
I mean did not sync although I am pointing to popular NTP protocols like Micorosoft, Google, Ubiquiti etc