In order to write and run the script in this answer I typed "Greenwich sidereal time right now?" into google (or at least tried to) and got two numbers.
Greenwich sidereal time was 09:51:07 but my local sidereal time was ten minutes earlier at 09:40:50.
I'm in UTC +8 so the ten minute difference is not because I'm ~8 hours away.
What causes this small difference in sidereal times?