fx rate change in cue

How to program a change of rate of an fx in two cues? Example:

In cue 1 the fx steps have a slow step time of 2 seconds each. When I press Go I want the fx step time to slowly(10 sec)  speed up to 0.5 sec each step. I tried with 2 different fx with same content but different steptimes but then the fx doesn't slowly fasten but fx2 fades in slowly and fx1 slowly fades out. 

Related