If you have an annual subscription, (which I believe is the only option for LrC), you can use it offline for as long as 129 days.
To get the longest possible offline period, sign out and back in just before you start travelling.
As others have said, make sure to be signed in when you leave home.
https://helpx.adobe.com/creative-cloud/kb/internet-connection-creative-cloud-apps.html?x-product=Helpx%2F1.0.0&x-product-location=Search%3AForums%3Alink%2F3.7.1
Creative Cloud for individual
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(Varies from 5 to 30 days)* + 99 days of offline use
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- After 30 days*, a dialog box requests an online connection.
- You can dismiss the dialog box; the next reminder shows up after 30 days.
- After 30 days + 69 days, the dialog box appears daily.
- After 30 days + 99 days, one final offline product launch is available.
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