"I think I'll take an afternoon dip in the pool before I go on that hike today."
It means to take a quick swim or get into the water for a bit, obviously in the afternoon.
An afternoon dip could also reference the dip in energy level that people feel due to the body slowing its metabolism in the afternoon (see Circadian Rhythms).
I have piano class in the afternoon
This is how you use yesterday in a sentence I went to the carnival yesterday afternoon
I feel groggy after an afternoon nap.
that dip is probably mild spicy!
This consignment must be delivered in the afternoon today.
Did you feel the tremor yesterday afternoon?
"John was online all afternoon updating is profile"
Mom baked bread all afternoon.
I like to eat humus. I dip my carrots into humus.
The tribes of the Atlantic traditionally catch fish on a Friday afternoon.
I took the afternoon off work because I had a splitting headache.
The football game started in a wet afternoon.