Carlos,
I have never used that option, so I do not have direct experience with it, but, THZ should be a fraction of an hour (according to the user manual) but it seems that it is not used by the model. From the source code, I can see that THZ is read but not used. RFDT is the amount of precipitation recorded in the time interval set with DTHY (in control table). Information in the file with RFDT is read only if INFL (in control table) is set to four (4). The file to be used must be listed in the file that in APEXFILE corresponds to the key FRFDT, and the ID number must be specified in the APEXRUN as seventh variable.
Best,
Luca