I am stunned and saddened by this decision. Surely Senior day (Friday) was a Bank Holiday?
I have ridden in more than one Senior race on a Saturday......after it was postponed from the Friday. They will have to be more than fortunate to get away with not having to cancel the race, over (say) a two or three year period. Certainly it can't run on Sunday. 
A) The riders will have gone home.
B) The Marshals will have travelled home.
C) The spectators will have largely disappeared.

If the thinking is that the visitors will stay there for longer, what is the reasoning behind the shortened Classic/MGP?

Absolute bonkers.