In my imagination...
They do spend time together (attending festivals, fireworks, cultural events, car racing, musical recitals, ...) but not as much as the inners spend by themselves doing everyday stuff like watching movies and eating chocolate-cream sundaes. This is largely due to the age gap and their differing interests.
Chibi & Hotaru (sometimes also with Pluto) spend a lot of time together.
Usagi, Minako & Rei spend a load of time together, generally trying to upstage one another in the silliest of ways.
Ami and Mako hang out a lot doing the quiet and thoughtful things that don't come naturally to the other 3.
Chibi and Usagi spend a huge amount of time together.
And of course Haruka and Mich spend an absurdly huge amount of time together too.
Haruka is still not allowed near Usagi (or anyone really) by herself or Michiru loses the plot which can lead to a lot less... holding hands.