In this case, ("When I saw") I think both are the same. But as Emir said, if you change the pronoun "I" to something else like "you", according to the pronoun you should change "gördüğümde". But no need to change "görünce". When I saw----> Ben gördüğümde When you saw----> Sen gördüğünde When I saw--->Ben görünce When you saw---> Sen görünce

Both have the same meaning but görünce mostly used by the third person O görünce ande gördüğümde are used by first and second person in the sentences

''Gördüğümde'' past tense. But doesnt matter. Usually meaning doesnt change.