Tom Riddle and the RoR - when

[hp_fan_2008]

No: HPFGUIDX 181776

Carol:
 
> Also, I don't think he would have brought the tiara to Hogwarts to
hide it when he had a job interview. Is he supposed to hide it under
his cloak in broad daylight? He'd have had to drop it off at the RoR
on the way to the interview, and to do that, he'd have needed to know
about the existence of the RoR already (it would be too much of a
coincidence for him to find it for the first time on the day of the
DADA interview), which means, he'd have had to find it as a student.
Only he didn't, so far as we know, hide any of the other Horcruxes
there, so what would he have used it for?

HP Fan 2008:

Actually, I believe that he hid the diary there originally. On the day
of the interview, he could sneak over to the ROR, switch Horcruxes,
hide the diary under his cloak, and then go to the interview. 
                     HP Fan 2008