One year [[after they got married]] they found his socks and car keys.
Marked Theme: circumstance of temporal Location realised by a nominal group with an embedded clause as Qualifier.
Note: The reason one year after is not a conjunction group, with one year as a Premodifier of after is as follows:
(1) conjunctions form a word class within the primary word class of adverbials [Halliday & Matthiessen 2004: 358];(2) Premodifiers in adverbial groups are grammatical items — there is no lexical premodification in the adverbial group [op cit: 356];(3) items serving as Premodifiers in adverbial groups are adverbs of polarity, comparison or intensification [ibid];(4) all the examples given of Premodifiers in conjunction groups are grammatical items (even, just, not, only), not lexical items [op cit: 358].
Consider, for example, the inutility of analysing the following as a conjunction group:
Thirteen excruciating mind-numbing minutes after (he began speaking) …