Question: why is 12pm after 11am?
Answer: As standard 12:00 AM is taken as the start of the day. Time of the day is divided in two halves (24hour= 12 hours before midday + 12 hours after midday) so the 11 AM is 11th hour before midday as clock strikes 12 again it changes to PM (after midday) so it's 12 PM after 11 AM and 12 AM after 11 PM.