When managed custom actions are embedded into the pre-complied native Custom Action DLL (sfxca.dll) using MakeSfxCA.exe, the timestamp of the DLL in the PE Header of the DLL (IMAGE_FILE_HEADER.TimeDateStamp) is not updated with the UTC timestamp for the date and time it is edited, but retains the timestamp from when it was originally compiled for the WiX distribution that it shipped with.
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2012-01-24 02:20:22 PST in Windows Installer...