NavList:

Did the bomb aimer and the navigator ever have a casual conversation while flying over the continental US?

In any multi-crew military aircraft there’s virtually no casual conversation.  Firstly, you’re too busy.  Your operating authority will have laid down strict operating procedures listing actions to be completed every so many minutes.  Secondly the whole crew will hear you, and at least one crew member will probably need to be working undisturbed; conference channels, if they exist and are used at all, are usually reserved for basic training with a screen crew member.  Thirdly, until the digital age, aircraft operating systems were approaching becoming a giant analogue computer, and each crew member was intent upon monitoring and tweaking his own particular input to ensure ‘the system’ was producing the most accurate results possible.  Finally, just like the watch keeping team in a ship should be constantly thinking “Is this ship safe?”, the crew of an aeroplane should be thinking “Is this plane safe?”.

With respect to synchronisation of watches, I suppose this might depend upon whether you needed the correct time or a common time.  I can think of situations for some military units in the field when the two might be slightly different, but within the RAF we used GMT, and it was up to every crew member to ensure their own watch was corrected to this before each flight from a master watch in the flight planning section.  Therefore, I don't think I ever heard the tern 'hack' used.  You were also advised to rate your watch although in my time most watches were accurate enough not to need this.
DaveP