You can try signing out and then back in again before you leave the office. The idea being it shouldn't need to check again for 28 days.
However this is not always guaranteed to work. Sometimes it just needs to do it continuously.
While on site if you have access to a wifi network or can connect your laptop using your phone you should be able to sign in and be good to go, until it decides otherwise.
I hate this system with a passion. My wireless connection is cellular and can be somewhat flaky and the number of times I have had to sign out and back in while actually in the middle of work is very aggravating. Just opening a second instance of SU can be enough for it to decide I'm not signed in.
If I was doing a lot of sitework these days I would probably keep a pre subscription copy on my laptop. Something that uses the older classic license, but even that I'm not so sure of.