9pm is 2100 hours Navy / Military time, which is based on a 24 hour clock system. 12am is 0000 hours, 1am is 0100, 12pm is 1200, 6pm is 1800 hours, etc.
3 oclock
12 oclock 6 oclock
In the evening when the sun is just about to set and you are relaxed and have a good book to read!
nine oclock and six oclock
at 9 oclock
9 oclock
2.00 oclock
12 oclock
at 11 oclock
6 oclock 7 ocklock or 8 oclock i am very not sure
"5 o'clock in the evening" and "5 o'clock in the afternoon" generally refer to the same time but can imply slightly different contexts. Typically, "afternoon" refers to the period from noon until around 5 PM, while "evening" starts around that time and continues until night. Therefore, if someone says it's 5 o'clock, they might be referring to either, but it's often more common to consider it evening.
10 oclock monday thru Friday 8 oclock on Saturday appointments only on Sunday