Hello Kikie,
Yes, the regular check in is 4.00 pm. but If you wanna just drop your luggages off, you can stop by after 13:00. But you might see my cleaning agent though.
Also my welcome booklet includes big coin locker locations information nearby, like the size of 843×355×575(mm) or 1200×355×575(mm). You may wanna use them to free your hand until your check in time.
Regards,
Tomoyo