INTRAZONAL SKIM values as interval or "LESS THEN" in PGM=Distribution

Is any way, how to distribute intrazonal trips not only with fixed time, but widely i.e. as a interval (0,28) or "<=28".

Background: Average trip duration is aprox 28 minutes (sociodem survey) and average intrazonal cost is in time is also 28 minutes. Standard computing of intrazonal trip in distribution use discrete number 28. I want use use 27,26,25 ... to 0 min.

classic discrete distribution code:
   SETPA P[1]= ZI.1.P1  A[1]= ZI.1.A1
   GRAVITY PURPOSE=1,  LOS=MW[40], FFACTORS=FF