This link states that:
When you use the present perfect tense you have to be talking about a period of time that you still consider to be going on. For example, if it’s still morning, you can say, "I’ve shaved this morning." If it is afternoon or evening, all of a sudden "I’ve shaved this morning" sounds really weird.
"I've shaved this morning" sounds more like past perfect, and indication of specific time (in the morning) makes this sentence incorrect. Am I spot on?
Then what is the difference between the construct of past perfect, present perfect and future perfect?