the standard way that I debug formula like this is to make lots of formulas that do just 1 part and display the results.
so I would probably create formulas like:
time({incident.u_duration_other})
and of course time(00,30,00) and time(00,31,00)
then if all of this works as expected (which I'm guessing it won't) you can start combining them like:
time({incident.u_duration_other}) <= time(00,30,00)
time({incident.u_duration_other}) > time(00,31,00)
etc
this is basically the only way that i can think of to see if CR is thinking/seeing the data the same that i thought it was.
HTH