Constraining widths of layout objects (TimeSignature)

[Hanns Holger Rutz]

I'm staring at

    
http://lilypond.org/doc/v2.12/Documentation/user/lilypond-learning/Size-of-objects#Size-of-objects

but there is no information about how to constrain the width of objects. I 
would like to adjust the width of a time signature. I randomly tried

    \score {
      \new RhythmicStaff {
        \override Staff.TimeSignature #'minimum-length = #23
        \set Staff.instrumentName = \markup { \char ##x00D7 1/4 }
        \time 1/16
        \times 2/3 { 
            c'32  c'32  c'32  
        }
      }
    }

but that doesn't seem to have any effect. I have independent scores with 
different time signatures, and they must have all the same layout width.

where would I look up all the possible overrides for Staff.TimeSignature?

thanks, .h.h.