I'll play football when I have had my dinner

I'll play football when I have had my dinner
 

When I have had my dinner
When I have my dinner
Why is only possible the first possibility?

Because the second one means that you will be playing football and having your dinner at the same time. Very bad for the digestion. For the correct time sequence, the dinner must be a completed action, hence perfect tense.

I wouldn't say either of them, by the way. I would say "I'll play football after I have had my dinner"

Except I wouldn't say that either. First, it is very bad to play football on a full stomach, and secondly, I would never play football anyway. :D:D

you can just say "I'll play football after dinner."

I'll play football Sunday morning before breakfast... (If I win my personal battle with the bedding sheets...)