You added a custom column to OneClick list view for the mGuardSysUpTime attribute but the value remains the same unless and does not increment. On the attribute tab for each device, you can view this attribute and it's it's possible to refresh this at the touch of the refresh button but there is no option on the list view to refresh or update the values displayed.
This is by design as the list view displays multiple devices and multiple attribute columns for each. Refreshing all of these at once could be impactful to performance if there are many models in the list view, so is not possible.
Logging out of the Oneclick client and logging back in will cause Spectrum to poll the devices for an updated value of these attributes.