Hello, @keziahsiscar! Actually, rather than OJT, supervised teaching in the Philippines is more commonly known as practicum. The supervised teaching practice required by AITSL is just a MINIMUM of 45 days. So since we usually have our practicum for ONE WHOLE SEMESTER (which in my case, from November to March, is approximately 95 school days), we definitely satisfy that prerequisite.
To give proof for this requirement, you'll just have to ask for certification from the school where you had your practicum and ask them to state the required details (duration of supervised teaching practice and age range of students taught).
Good luck!
EDIT: So if you're sure that you definitely had 300 hours of teaching practice, if converted to number of days, then that is only 12.5 days. But of course, we'll also have to take in consideration that the conversion was divided by 24 hours. Obviously, we only spend a certain number of hours in school for practicum. I'm sure that your school (where you had your practicum) will be able to answer your queries regarding the duration of your teaching practice.