extra days of slide lock

In https://slideme.org/slidelock,
I have found following.

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However, you will have to keep in mind that your users may be traveling, that means they will most likely be in roaming and/or may not use networking, so your license fetch/refresh will not work. In this case you could go for a predefined grace period, for example (let’s say you let the end-user use the app for X extra days even if you can’t fetch the license during this period).

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How can I decide the extra days for my app?