In cases where tracks have been recorded in different studios, by different engineers or even performed by different players a different EQ may need to be set for each song. This usually takes up the most time in the mastering session. This helps get the most level out of the digital source. This is the only sample rate for CD's at this time. However, if you are not happy with a fade it's usually a lot easier and cheaper to redo the fade during mastering rather than to re-mix the entire song, especially if you are happy with the mix in all other ways.
Fades are a fairly quick process.
This is always done during mastering. It assures there are no clicks or pops in the production of the CD's. This process does not take very long. Clients should not be concerned if the masters are out of order, as long as they know they will be getting their project mastered. Sometimes the client is not sure of the order they want.