Getting a data from a order at hookUpdateOrderStatus

[thiagorobis]

I have a question on building a module.
I need to calculate the difference in days between a status and other status changed then send an e-mail notification.
For example, if between the date of purchase and today went up to 10 days, send e-mail. Otherwise, do not send e-mail.
I'm trying to implement this function using a module and calling the hook hookUpdateOrderStatus.
However, I am not able to get the date of the order in question, so the function is not working.
I try used this one, but dosen't work at all:

$order->date_add;

AND

$params['date_add']

One would like to help please.
Grateful