I have never seen a random time axis, so am scratching my head a bit here.....
This is the config for a 24 hour trend in my groov build;
You can change the scan rate to match the data granularity you need, it will not affect the overall time axis.
In this case, I am getting the pen data every 30 seconds.
Perhaps you mean the time printed on the axis, and not the axis duration?
If so, we need to know if you have groov Server for Windows, or if you have a groov Box (AR1).
For groov server for Windows, check if your PC is not auto updating by a third party application or swapping between time zones.
If it is a groov Box, log into groov Admin and check the system time tab under the 'system' menu option.
Make sure you have it set to your timezone and your time synch is set to once a day.