+1 to something that will "Show Buff Time Remaining on Friends Island"
Whether the tooltip should appear on hovering or after clicking, or even on another part of the screen should be evaluated on test... Why not here (where this is room to say "Buff expires xxxminutes after you visited the island":
If for performance reasons the time has to be the time remaining when I first arrived then that would be acceptable (not as good, but still very worth having)