One thing its clear, combat turns are definitively not days. I mean, a ship can only fire its guns once a day? and needs 3 days to reload its CSM launching tubes?
And how come you can fight with the same ships several times in the same sector during the same game turn using the full 30 combat turns?
So I belive a combat turn its less than an hour, probably a minute. Yes, a 30 minutes space combat make sense, and firing Meson BLasters every minute, and reloading the CSM in 3 minutes.
Now, that brings up of course that the combat map its not exactly a sector from the main map, but just the fraction from the sector where the 2 fleets meet.
About planet size, you have to assume that its been scale up for easy recognition on the map.
Now it all make sense......