Format is the same as `date -R` as documented in the Debian Policy:
"
The date has the following format [8] (compatible and with the same
semantics of RFC 2822 and RFC 5322):
day-of-week, dd month yyyy hh:mm:ss +zzzz
where:
* day-of week is one of: Mon, Tue, Wed, Thu, Fri, Sat, Sun
* dd is a one- or two-digit day of the month (01-31)
* month is one of: Jan, Feb, Mar, Apr, May, Jun, Jul, Aug, Sep, Oct, Nov, Dec
* yyyy is the four-digit year (e.g. 2010)
* hh is the two-digit hour (00-23)
* mm is the two-digit minutes (00-59)
* ss is the two-digit seconds (00-60)
* +zzzz or -zzzz is the time zone offset from Coordinated Universal Time (UTC).
“+” indicates that the time is ahead of (i.e., east of) UTC and “-” indicates
that the time is behind (i.e., west of) UTC. The first two digits indicate
the hour difference from UTC and the last two digits indicate the number of
additional minutes difference from UTC. The last two digits must be in the
[...]
[8] This is the same as the format generated by `date -R`.
"
https://www.debian.org/doc/debian-policy/#debian-changelog-debian-changelog
