Office 365 whenCreated and whenChanged report. Find user creation date on Office 365.

This reports the created date of every user in your organisation.

$objUsers = get-mailbox -ResultSize Unlimited | select UserPrincipalName 

Foreach ($objUser in $objUsers) 
    {     
        $objUserMailbox = get-user -Identity $($objUser.UserPrincipalName) | select identity, whenCreated, whenChanged

$strUserPrincipalName = $objUser.UserPrincipalName
$strWhenCreated = $objUserMailbox.whenCreated
$strWhenChanged = $objUserMailbox.whenChanged
write-host "$strUserPrincipalName : $strWhenCreated : $strWhenChanged"
    }

Copy and paste it into the PowerShell after connecting and then press enter twice.. Should show you a list of users and their Created time and last modified time.

Hope this helps someone.