diff --git a/ui/dr-ui/src/merge.rs b/ui/dr-ui/src/merge.rs
index 0dd713a..370d5a8 100644
--- a/ui/dr-ui/src/merge.rs
+++ b/ui/dr-ui/src/merge.rs
@@ -518,7 +518,16 @@ fn run_inner(
     let black = first.raw.black_level[0];
     let white_level = u32::from(first.raw.white_level.saturating_sub(black)).max(1);
     let profile = dng_profile(first, white_level);
-    let (_, carried) = crate::export::header_for_file(&first.meta);
+    let (_, mut carried) = crate::export::header_for_file(&first.meta);
+    // The composite is dated at the middle of its sweep — the mean of the
+    // frames' capture times — so it sorts among the frames it was made
+    // from, not at the first of them and not at the moment of the merge.
+    // The zone is the first frame's; a sweep does not cross one.
+    let stamps: Vec<i64> = frames.iter().filter_map(|f| f.meta.captured_at).collect();
+    if !stamps.is_empty() {
+        let sum: i128 = stamps.iter().map(|&t| t as i128).sum();
+        carried.captured_at = Some((sum / stamps.len() as i128) as i64);
+    }
 
     let output = MergeOutput {
         projection,