On the same day it is 12 hours
12am is midnight. 12pm is noon.
Strictly speaking, there is no 1200 PM. There's 12 noon and 12 midnight. 12 noon is 1200 hours.
There is no such time as 1200 am: there is 12 noon and 12 midnight. The question cannot, therefore, be answered.
Technically, 12 PM doesn't exist. It's either 12 noon (3 hours) or 12 midnight (15 hours).
It is normally considered to be 2 hours, as 12pm is normally considered to represent noon.Note that technically "pm" stands for Post meridiem (in Latin) which would mean "after noon". So 12pm would be 12 after noon, or midnight. However 12pm being noon is the norm.
AM is from midnight to noon and PM is from noon to midnight. AM and PM are twelve hours each, adding up to twenty-four hours.
12 hours
From midnight (am) to Noon (pm) is 12 hours.
12am is midnight. 12pm is noon.
From midnight (am) to Noon (pm) is 12 hours.
Technically, 12 AM doesn't exist. We refer to 12 noon or 12 midnight. From 6 AM, it is six hours till noon, and eighteen hours till midnight.
Midnight to noon is 12 hours (AM), noon to midnight is another 12 hours (PM). Therefore, it is 12 hours from PM to AM.
There are 12 hours as am and 12 hours as pm. This in total makes 24 hours a day. for 24 hour time, from 12 midnight to 12 noon it is am. Then pm hours start from 12 noon to just before 12 midnight. The change from am to pm is in one moment.
Midnight is neither am not pm. It is "twelve midnight".
pm
A normal clock has twelve hours and it goes through two cycles of that period every day. There are occasions when you need to know whether it the time referred to is in the fist cycle (midnight to noon = am) or the second (noon to midnight = pm).
Number of minutes since midnight = 9*number of minutes since noon. So number of minutes since midnight = 9/(9+1)*number of minutes between midnight and noon. = 0.9*number of minutes between midnight and noon. = 0.9*time between midnight and noon. = 0.9*12 hours. = 10.8 hours. = 10 hours and 0.8*60 minutes = 10 hours and 48 minutes. So the time is 10:48 am