If you look at "man git-commit-tree"
While parent object ids are provided on the command line, author and committer information is taken from the following environment variables, if set:
GIT_AUTHOR_NAME
GIT_AUTHOR_EMAIL
GIT_AUTHOR_DATE
GIT_COMMITTER_NAME
GIT_COMMITTER_EMAIL
GIT_COMMITTER_DATE
(nb "<", ">" and "\n"s are stripped)
In case (some of) these environment variables are not set, the information is taken from the configuration items user.name and user.email, or, if not present, the environment variable EMAIL, or, if that is
not set, system user name and the hostname used for outgoing mail (taken from /etc/mailname and falling back to the fully qualified hostname when that file does not exist).
A commit comment is read from stdin. If a changelog entry is not provided via "<" redirection, git commit-tree will just wait for one to be entered and terminated with ^D.
DATE FORMATS
The GIT_AUTHOR_DATE, GIT_COMMITTER_DATE environment variables support the following date formats:
Git internal format
It is <unix timestamp> <time zone offset>, where <unix timestamp> is the number of seconds since the UNIX epoch. <time zone offset> is a positive or negative offset from UTC. For example CET (which is
2 hours ahead UTC) is +0200.
RFC 2822
The standard email format as described by RFC 2822, for example Thu, 07 Apr 2005 22:13:13 +0200.
ISO 8601
Time and date specified by the ISO 8601 standard, for example 2005-04-07T22:13:13. The parser accepts a space instead of the T character as well.
Note
In addition, the date part is accepted in the following formats: YYYY.MM.DD, MM/DD/YYYY and DD.MM.YYYY.
Edit see this repo and screenshot:
* https://github.com/yeukhon/demos/commits/master/git-date
* https://github.com/yeukhon/demos/blame/a9fc9dfe6d35c5ffe14af...
* https://github.com/yeukhon/demos/commits/a9fc9dfe6d35c5ffe14...
You see I got a 3 minute (using local time) and then 4 hours ago because I set the timestamp manually in the most recent commits. So yes you can set time in the future / past.