There is a lack of consistency in what we might consider normal...
"Meet me at [whereever] in 2.75 hours."
And when was the last time someone said to you, "I'll be done in 1 hour, 30 minutes"? It seems more natural to say "an hour and a half" or "90 minutes".
I propose that we're good at only dividing an hour in half. Any more (thirds, quarters, tenths) and we prefer minutes. Tenths are particularly problematic, because intervals of six minutes are not very intuitive.
I've often wondered why we've failed to move from base60 for seconds and minutes and base24 for hours. Sure, in the days of the sun dial, it was (is?) convenient to divide 360 degrees into 15 degree intervals (for a total of 24 intervals). But why divide 15 degrees into 0.25 degree intervals (for a total of 60 intervals)? And why divide 0.25 degrees into 0.004166... intervals (for a total of another 60 intervals)?
And 60 Hz AC power... what's up with that? 110 (120?) Volts?
Oh... but I digress!
Scott-
P.S. If anyone's taking a vote, I choose hh:mm.
Scott-