Script to pull all the mailboxes created in 24 hrs on Exchange 2010

Get-Mailbox -ResultSize unlimited | Where {$_.WhenCreated -gt (Get-Date).AddDays(-1)}

If you need the details for 1 week, replace 1 with 7

Get-Mailbox -ResultSize unlimited | Where {$_.WhenCreated -gt (Get-Date).AddDays(-7)}