PBW - Fleet movements?

[Davout]

I have two of my Fleets 3 spaces away from an Enemy Planet stacked together. I select both Fleets(with the Shift button) and tell them to attack/move to the Enemy Planet.
Question: In PBW, do my 2 Fleets arrive at the same time and both attack the planet or first Fleet arrives and attacks the planet, then 2nd Fleet arrives and attacks the planet?

In my solo-turn based games both Fleets arrive and attack at the same time, but with limited experience of my PBWE game, it seems to work differently.

I like to group my ships into Squadrons and not Fleets, but if different Fleets attack seperatly in PBW games then I will have to change my groupings(but I like the Squadron formations better!! May be one of the fixes could be: Ships can be grouped into Squadrons or Fleets, and Squadrons can be grouped into Fleets...that would be NICE!)

Thanks in advance.