Not sure if you noticed it. The wierd bug that you fixed in the demo with a OnUpdate function that you call onPlay and disable it thereafter can be fixed by just calling :Pause() after :Play().
What cannot be removed though is the delay. No clue why it does not animate without it.
Lua Code:
--animationgroup
local group = wedge:CreateAnimationGroup()
local rotation = group:CreateAnimation('Rotation')
rotation:SetOrigin('BOTTOMRIGHT', 0, 0)
rotation:SetDuration(0)
rotation:SetEndDelay(1)
group:Play()
group:Pause()
spinner._rotation = rotation