It obviously depends on how quickly it is played, so it will vary somewhat. But roughly: The first movement is about 19 minutes, the second is 7 and the finale is about 10 minutes. That is 36...
There is an infinate ways to modulate from C major to D major.One way in which you can do this is use a "pivot chord" which is a chord that is similar in both keys. The chords similar between these...