Is VCT(volts center tapped) voltage between two outer taps or betwen outer tap and center tap?
For example: will 241-8-24 give me 24V between center tap and outer
  tap or between both outer taps?


Answer: between both outer taps is 24 volts.

The device you listed has a secondary voltage of 24 volts and a centre tap so, if you were to use the centre-tap and one of the outer connections to the secondary you would get 12 V RMS out. Another way of describing this output that is sometimes used is "12-0-12". This implies that you get 12V AC either side of the centre tap that is referenced (for convenience) as 0 volts.