High Sierra beta (10.13.5 beta 2) kernel variable changes

Is it normal for the kernel variable kern.boottime to change between startup and shutdown. I have a script, run as root, at startup time, by launchd which records kern.boottime in a log file sysctl -n kern.boottime >>/usr/local/data/boot.log If I execute the same command, in Terminal, after logging in a few minutes later, the value has changed (now indicates 3 seconds earlier.) I have done this several times in the last couple of macOS releases and the same 3-second difference is noted. Does this sound like a bug, or purposeful? Thank you in advance.

Update: Does not occur every startup. I am trying to determine the circumstances where it occurs consistently.

In this post, System Uptime | Apple Developer Forums

eskimo discusses kern.boottime, saying

Be aware that this time will change if the system clock changes, that is, the value is the boot time relative to the current system clock.

And the system clock might be updated via network time server when the system connects or reconnects to a network.

High Sierra beta (10.13.5 beta 2) kernel variable changes
 
 
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