Get the time and date of git tags

One more option:

git for-each-ref --format="%(refname:short) | %(creatordate)" "refs/tags/*"

See https://git-scm.com/docs/git-for-each-ref#_field_names for format options

%(creatordate) gives the date of the commit pointed to, to see the date the tag was created on use %(taggerdate)

You can incorporate the shell directly:

$> git for-each-ref --shell --format="ref=%(refname:short) dt=%(taggerdate:format:%s)" "refs/tags/*"

ref='v1.10' dt='1483807817'
ref='v1.11' dt='1483905854'
ref='v1.12.0' dt='1483974797'
ref='v1.12.1' dt='1484015966'
ref='v1.13' dt='1484766542'
ref='v1.2' dt='1483414377'
ref='v1.3' dt='1483415058'
ref='v1.3-release' dt='' <-- not an annotated tag, just a pointer to a commit so no 'taggerdate', it would have a 'creator date'.
ref='v1.3.1' dt='1483487085'
ref='v1.4' dt='1483730146'
ref='v1.9' dt='1483802985'

Note that both of the above solutions get you the commit date, which can be wildly different than when that commit was tagged for release. To get the date of the tag itself, you've got to find the tag itself with rev-parse, read it with cat-file, and then parse it. A little pipeline:

git rev-parse v1.0.0 | xargs git cat-file -p | egrep '^tagger' | cut -f2 -d '>'

Use the --format argument to git log:

git log -1 --format=%ai MY_TAG_NAME

This always worked for me:

git log --tags --simplify-by-decoration --pretty="format:%ci %d"

Consult the "PRETTY FORMATS" section of the git-log manpage for details of the format string if you want a different date formatting.