Wrote time adjustment tool for WSJT-X on Linux (gtk+). It can change system time and interact with the NTP (or equivalent) services to turn on/off automatic clock updating:

I tested it on Arch Linux but it should work on other distros as well. One annoying pending issue is still that when turning NTP back on, it prompts for root password. The code can be found from github.com:

https://github.com/jmeloranta/timeadj

Compile with: make
And install with: make install

By default it installs under /usr/local directory. Needs gtk+ graphics library.