I don't find that to be true. I'm dehydrated and all my waterskins are empty whenever I login after being offline for 4+ hours.
As far as being safe while logged out you need to be in a completely enclosed room that doesn't have any surfaces on the outside of your base. Put your "safe" room up on at least the 2nd floor of 3 or more and put it in the middle of at least a 3x3 floor. Basically if you think of it as a cube you want the 6 cubes that share faces with it to also be inside your base.
I sleep on the 4th floor of a 5 floor base and I break the ladders/ramps behind me when I climb up for the night and replace them when I log back in. If you're up that high and there are no ladders/ramps they can't build any themselves so if they want to get you they have to come in through the roof with flying mounts or break every bit of supporting structure beneath you to collapse your safe room.
Also you don't want anything on the first 2 floors inside your base against the outside walls. People can see that stuff by fiddling with camera views. If your refinery is against an outside wall you'll come home one day to find just the wall it is next to broken and any metal you had in it gone.
Lastly the best defense is a large tribe. The more people you have around your base the less chance a cat burglar/assassin can get in undetected. Raptors set to aggressive in an external courtyard around the base seems popular too but those aren't really that hard to deal with. I think there will be a lot more theft than PvP in the days to come.