the difference between 12:30am and 12:30pm | Learn English

The day is divided into two periods: a.m. (from Latin ante meridiem, meaning, before midday) and p.m. (from Latin post meridiem, meaning, past midday).

12:30 a.m. is in the first period which begins at midnight (technically 12:00 a.m.) and the 12:30 p.m. is just after noon (which technically is 12 p.m.).
To avoid confusion, many people do not use 12 a.m or 12 p.m. and prefer to use midnight and noon.
Afternoon begins at noon and runs until evening. Different cultures and even individuals define the time it ends in different manners. Most of the time, they consider afternoon to end when the sun sets but sometimes people will base it on a certain time. I personally feel we have much more important things to worry about than when afternoon ends and don’t recommend wasting time worrying about it.