My time zone is set to "America/Los Angeles" here, and it currently says (correctly): "Server time: 11:35 Local time: 04:35" (the server is in UTC and local time here is UTC-7 (PDT) during DST).
When hovering over a "hist" link in a contribs or page history list (e.g. this), the time column shows times that are an hour early (02:59:40 in this example, for an edit that occurred at 10:59:40 UTC = 03:59:40 PDT).
When hovering over the "diff" link for that edit (here), it shows: "New Revision 2019-05-11 02:59:40", also an hour early.
When hovering over that page title at 11:43 UTC (04:43 PDT) (here), though, it correctly calculates: "43 minutes old".
Another example: hovering over this, shows:
New revision 2019-05-02 19:07:25
Old revision 2019-02-27 09:32:42
The New time (during DST) is wrong but the Old time (not DST) is correct – both are calculated as UTC-8.