time clause

Will it be grammatically correct to substitute the Present Perfect for the Present Simple in the time clauses of the following sentences?

When we have had tea, we'll go for a walk.
When we have tea, we'll go for a walk.

Are both of the sentences right or not?

Both are grammatically OK, but they mean different things.

Dear SoothingDave
could you specify the difference in meaning, please?

#1 means we will go for a walk when we have finished having tea.
#2 means we will go for a walk at the same time as having tea (an unlikely situation).

If you replace "When" with "After" in both sentence, they will mean the same as #1.

After we have had tea, we'll go for a walk.
After we have tea, we'll go for a walk.