'before RepeatTrial
nDur = 17
'after RepeatTrial
c.SetAttrib "StimDur", nDur
Then increase it by 17ms each time it is ran (for example). To do this, you would change the Mouse Input 2 (Allowable 2) (this indicated an incorrect response) End Action to Terminate. Then add an InLine after the CaProcPostMask. If the InLine, you can use the following script:
If CAProcPostMost.RESP = "2" Then
nDur = nDur + 17
GoTo RepeatTrial
End If
Please see INFO: Declaring a global variable in User Script (Video How-To) and E-Prime How To: Advanced Attributes.