diff --git a/HellionChat/Ui/Components/TimestampColumn.cs b/HellionChat/Ui/Components/TimestampColumn.cs
new file mode 100644
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--- /dev/null
+++ b/HellionChat/Ui/Components/TimestampColumn.cs
@@ -0,0 +1,17 @@
+namespace HellionChat.Ui.Components;
+
+// TEST-MIRROR: Ui/TimestampColumnTests.cs
+//
+// The timestamp sits in a column of fixed width so the sender names below each
+// other actually line up. The mockup asks for tabular figures; ImGui exposes no
+// font features, and whether the bundled face even has equal-width digits is
+// unverified. So the width comes from measuring the widest shape the format can
+// produce, once per layout change rather than per row.
+//
+// Eights, not zeroes: in most faces 8 is the widest digit. A column measured
+// from 00:00 would be undercut by a 10:38 and shove the name column right on
+// that one row -- exactly the misalignment this exists to remove.
+internal static class TimestampColumn
+{
+    internal static string SampleFor(bool use24Hour) => use24Hour ? "88:88" : "88:88 PM";
+}