12 pm what time is it?
To avoid confusion, it is always better to use the 24-hour clock, so that 12:00 is 12 noon. Therefore 24:00 Sunday or 00:00 Monday are both midnight meaning Sunday to Monday. It is common for transport timetables to use 23:59 Sunday or 00:01 Monday, or 11:59 pm or 12:01 am, to further reduce confusion.