Seems like an awesome idea at first and then I realize everyone including myself would wake up/stop work/etc every four hours to log in and do this. :)
That'd be a really cool mechanic, but the new day refill would probably unbalance it :P Making for very easy energy and mood stockpiling even who not really playing.
What if we could actually "break off" a piece of our energy tank or mood tank and set it aside for later? Say you start a new day with full capacity 1500/1500. Then you have the option to split off, say, 500 of each tank, leaving you with 1000/1000, and they each would take up a slot in inventory. Then, in a pinch, you could reattach the piece(s) for a 500 mood or energy boost.
Edit: If you died, however, the split-off tanks would automatically empty and be reattached, still leaving you with 0/1500 of each.