Currently you do not specify a number of days for offline use. The number of days for which your Named User license is valid is determined by its expiration date, whether online or offline.
You can check the "Expires" field on Pro's Licensing tab:
You do need to be careful when checking out a Named User license for offline use near its expiration date. You won't be able to work offline once your license expires. So you'll either want to renew your license early enough to get a Named User license for the next license year, so it covers your time offline, or ensure you have a way to temporarily get online and renew it.