The point about MDIs (Minimum Departure Intervals) is quite correct but you probably didn't have one imposed on you or that is what the Tower Controller would have told you.
Stupid as it seems, CFMU slots often come through when planes are at the holding point. My own personal method to deal with it is selective deafness when I'm told.
And are there really aerodromes WITHOUT clearance delivery? How quaint.
P7