Returns the installation date for an app installed uisng an Apple Installer package. In Terminal run /path/to/script /path/to/Bundle.app (drag the app into the window).

Get App Install Date.zsh

#!/bin/bash

# in Terminal run /path/to/script /path/to/Bundle.app
installedApp=$1

# get the app's bundle identifier
bundleID=$( /usr/bin/defaults read "$installedApp/Contents/Info.plist" CFBundleIdentifier )

# get the installation epoch date for the bundle identifier
installEpoch=$( /usr/sbin/pkgutil --pkg-info="$bundleID" | /usr/bin/grep "install-time" | /usr/bin/awk '{ print $2 }' )

# convert epoch date to user-readable date and return the result
echo Installed: $( /bin/date -j -f "%s" "$installEpoch" )

exit 0