It wouldn't be very realistic, if the time scale was 1:1 in Oblivion then you would be able to run across all of Cyrodill in 15 min. The game world would feel so small.
Guess what? With Cyrodiil size in TES4 (esspecially knowing REAL size of Nirn, and Cyrodiil in particular), time scale should be about 1:400 to actually fit time consumption during travels
This way each 3-4 real minutes would be new day in game (just imagine how fast sun and moons should move)
http://images4.wikia.nocookie.net/__cb20091105224341/elderscrolls/images/2/2c/Nirn_Map.jpg
Pay attention to scale that is showed in lower left corner (and do some quick math)
So either way it is unrealistic.