The date/time written to index.xml and index-v1.json should always be in
UTC format. These formats are often in the form of just a date, e.g.
2019-04-28. Those are then converted to UNIX seconds, which includes the
time. In the date only case, the time is assumed to be 00:00, which will
be different per time zone.
index-v1.json is better since it mostly uses Java-style UNIX time in millis
but the dates/times are parsed then stored in the local database in the old
format yyyy-MM-dd_HH:mm:ss which will result in different UNIX times when
the device is in different time zones.
fdroid/fdroidclient#1757
1d359f82ce