It looks like you are looking for a feature that is not there. Check Point will be able to confirm.
@BarYassure Can you help us out here?
Andy's last suggestions looks good but you could set up a specific Filter on the Last Connection column and set the From and To to be the last half an hour (for example).
That should show Endpoints not connected in the last half an hour (or hour, or more depending on your time frames).
I have attached a couple of screenshots but you just need to hover the mouse over the Last Connection column to see the three dots that will give you the menu to create the filter.
I have found that the Last Connection time for online machines is usually 3 to 4 minutes behind the current time but if you refresh the view (circular arrow in the top right hand corner below the username) then it is only one minute behind the current time for currently online machines.
Otherwise just sorting the Last Connection column might be able to show you what you need.
I looked at setting up a Custom Dashboard but the only option I see is the Active/Inactive (Total endpoints), which is not useful in this case.