I will have little to report, I think, since I am leaning toward changing the flight for one main reason. If I do not go through passport control right away and wait for 5 hours, my checked in luggage will be circling around the carousel unattended (I am assuming I can't get my luggage before the passport control).
Don't worry about this; you will never get this far
No airline will allow you to board their flight to Russia with an invalid visa - the airline may get fined and may have to transport you back. Forget about trying to explain that you will be walking around for 5 hours until your visa becomes valid.
Having been to Russia 6 times already, trust me your passport and visa will be scrutinised when boarding the flight.