ICMP Timestamps are not controlled with a sysctl kernel adjustment like tcp timestamps, but rather need to be filtered by your firewall. There are two types of ICMP timestamp packets, a timestamp-request and a timestamp-reply, both of which can be filtered with iptables (or firewalld example coming soon).
iptables -A INPUT -p ICMP --icmp-type timestamp-request -j DROP
iptables -A INPUT -p ICMP --icmp-type timestamp-reply -j DROP
You can persist this by adding the lines to your /etc/sysconfig/iptables file.
Append the following lines to the bottom.
-A INPUT -p ICMP --icmp-type timestamp-reply -j DROP
-A INPUT -p ICMP --icmp-type timestamp-request -j DROP
If you have not previously run the commands above manually, restart iptables to have it reload this configuration file to take affect.
You can test this is working properly with hping.(Comments)