[Gare]

Or maybe they mean "day" as starting from UTC midnight.

[buescher]

I'd guess that's actually more likely. Interesting bit of jargon.

[sevensor]

Maybe they’re contrasting with sidereal days?

[chgs]

That was my initial thought, but that’s a difference of 10 mins over 3 days, and that’s orders of magnitudes more precise than should be used.