Simple suggestion, could the sleep "zzz" be added to buildings with a production queue and island buffs if they either have nothing queued or if the island buff is off cooldown.
So this would mean the sleep "zzz" indicator showing on the following if they are not producing anything:
Barracks
Elite Barracks
Combat Academy
Combat Armoury
Provision House
Rarity Provision House
Bookbinder
Snack Stand
Laboratory
etc
and the same showing for the following when the island buffs are available to use:
Spring Park
Footie Pitch
etc
would probably need an option to enable/disable this adding to the options for those that -1 or hate this idea.