Dates Not Sorting Correctly in Pivot Table

Here is how my Pivot Table is set up.

\1
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The way my dates are derived in the source data comes from an equation that converts the UNIX timestamp in Column C to PST.

=IF(ISBLANK(C2),"",(C2/86400)+25569+($H$1/24))

When I group by day, and attempt to sort, it changes the date format and will not sort correctly. Any ideas here?