Is it grammatical to combine the present perfect tense with time? E.g.
I've seen that movie two days ago.
I've completed the 12-step program last summer.
The deadline was two days ago, and I've finished the project ahead of time.
It is conditional and not done always.
According to this online resource,
Michaelis (pdf ~372kB)
Yet, both the above can be used and can be grammatical in certain contexts depending on the semantics.
We also use the present perfect with a time expression in the future as in:
Generally we do not use any time expressions, according to yet another:
Now that's an over-simplification.
Perfect present tense is used to indicate whether or not an action has already been completed, but not to specify when exactly it was completed. If you want to say when an action was completed, use past tense.