Translation:Call me immediately after you have met him.
Native English speaker here. This sentence makes sense. The person is telling the other person to call them a certain time. When? After something has happened, thus the need for a tense in the past.
See here: http://www.englishpage.com/verbpage/presentperfect.html. The present perfect tense is used for a time period in the past, not the present, thus it is applicable here.