They all mean the same thing, Chalew. ' With the present perfect form ('have finished'), the speaker is subconsciously viewing the situation from the present, while the simple present 'finish' is out of the consideration of time, from the speaker's viewpoint: it is merely a reference point for leaving. This is not a distinction that the speaker can consciously choose as he is speaking, and it has no effect on the listener; therefore, these sentences are all functionally synonymous.
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