Date format for maximum wall clock time

Hi,
I have a problem in passing the right format for setting the hard wall clock time. I've been successful in passing the hours and minutes, but I'm not able to set the seconds. Is it possible?
For now I'm passing the string formatted as follows: "HH:MM", but if I add the seconds "HH:MM:SS" it will just pass 0:00 to SLURM.

Thanks,
Alessio