I assume that you are familiar with (simple) FrameMaker usage and the design of simple XML DTDs. I don't know how much time it would take you learning FrameMaker from scratch, one full day maybe with some help. The same goes for XML (if you are familiar with the idea of grammars and data-structures). Otherwise count more !
Also, if you just opened the F+S Box, you might want to learn how to use F+S as an author (there is a printed book for that). It will take you about an hour to get the idea: instead of defining and using paragraph tags you will use a structure view and an elements list that someone designed for you:). Make sure that you understand:
Make sure that you know to insert, delete and move elements and attributes. I found inserting particularly difficult. Moving and deleting is easy, particularly if you configure the Text Window with Menu: View->Element Boundaries [as tags] .
I also did short tutorial called. See: http://tecfa.unige.ch/guides/xml/frame-sgml/ which you may want to consult