Should I use AM or am in the example below and what's the difference?
He came her at 3.20 AM this afternoon to deliver a pizza for me.
Hi, Cristi—Your sentence is a contradiction in terms. The time 3:20 a.m. is a time in the morning, namely, three hours and twenty minutes past midnight. If you wish to refer to "three hours and twenty minutes past noon," use "3:20 p.m." You can punctuate the numbers and letters in accordance with local custom.