Prepaid Modem enquiry

[C1ph3r]

I plan on buying this prepaid modem (https://www.telstra.com.au/internet/mobile-broadband/prepaid/telstra-pre-paid-4gx-wifi-plus?sacid=71...) before I go away and was wondering how exactly it works. When do the thirty days start, when I first turn it on or when I buy it? I'm not going away until mid feb and so I want to get it before the price goes back up and hold onto it until I need it.

[cf4]

The 30 days start from when you activate the modem's SIM. There will be an expiry date written on the box and the SIM will need to be activated before expiry date.