Setrange on a time field

Hi everyone,
I am using a custom table, among fields are "Starting time" and "Ending time" (both of type time).
I want to add some checks to avoid overlapping between times.
I tried to use the same code as in standard NAV table 99000752 (Shop Calendar Working Days) for validating "Starting time" and "Ending time".
I put the following code in a function:

recXXX.SETRANGE("Starting Time",0T,"Ending Time" - 1);
recXXX.SETRANGE("Ending Time","Starting Time" + 1,235959T);
IF recXXX.FINDFIRST THEN
  ERROR('Conflict!!!');

and called the function in the OnValidate triggers of both fields.
The problem is that I keep getting the following error message:

The time is not valid

The debugger stops at the first instruction.
What shall I do?
Thanks in advance