To express a time of day: 'in' vs 'on'?

Question

1. Please explain and simplify the 1st two paras herefrom?

The choice of prepositions depends upon the temporal context in which you're speaking. "On ~ afternoon" implies that the afternoon is a single point in time; thus, that temporal context would take the entire afternoon as one of several different afternoons, or in other words, one would use "on" when speaking within the context of an entire week.

"In ~ afternoon" suggests that the afternoon is a temporal space in-and-of-itself, wherein anything that happens will happen amongst many other events. In other words, the temporal context for this usage would be if one were speaking of a single day -- whether past, present, or future -- and of a single afternoon, during which many things might happen.

http://forum.wordreference.com/showthread.php?t=869146&p=4645217#post4645217

In your example, on the afternoon of that day = (on) that day's afternoon
= (on) that day, in the afternoon = in the afternoon (on) that day.

I don't know a rule for it. Sometimes only "on" fits the context, sometimes only "in", sometimes no preposition is allowed, and sometimes we have a choice...

The prepositions in the alleged sequence of equalities confuse me. 2. The first phrase uses on the afternoon, but which contradicts in the afternoon in the last phrase?

3. If you start with the first phrase and proceed forwards, then how did on capriciously change into in? If you start with the last phrase and proceed backwards, then how did in capriciously change into on?

Answer 1

When did you first meet Mr Holmes?

-- I met him on June 10th of last year, and if I recall correctly, it was in the afternoon, because I do remember feeling terribly bloated after a bad lunch.

And where were you on the night of June 10th of last year?
-- I was at home, feeling rather ill with food-poisoning.

In = during a specific part of the day ("I met him in the afternoon")

On = refers to the calendar day ("on the night of the 10th of June")

Answer 2

I also found this problem, in the afternoon versus on the afternoon. There are two concepts concurring, in + time of day and the concept on that day.

But I think the handling is simple. We say "in the afternoon" when there is no further indication.

• We'll meet in the afternoon.

We say on the afternoon when an of-indication follows.

• On the afternoon of my encounter with Peeta Mellard (The Hunger Games).