If you want to change all the reporting to minutes, you can customize the time units in HydroCAD:
1) Open the project
2) Select Settings|Units
3) Click Custom
4) Scoll down and select the "RealTime" parameter
5) Change the maximum value to 9999
6) Change decimal places to zero
7) Change the short symbol to "m"
8) Change the long symbol to "mins"
9) Change the scale factor to "1/60"
10) Click OK
11) Repeat steps 6-10 for "TimeInc"