yast2-ntp-client from YaST:SLE-15:SP3 project
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Add repository and install manually
For openSUSE Leap 15.3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/YaST:SLE-15:SP3/openSUSE_Leap_15.3/YaST:SLE-15:SP3.repo zypper refresh zypper install yast2-ntp-client