offline delay
Not possible.
Offline means that the device (or an intermediary IP router or NAT gateway) has cleanly torn down the connection. It is important to know that there is no active socket (connection) between Traccar and a device, because it means thay any sent commands will be queued until the device is next online.
You could alter the source code to hide the status completely, but really the question here is why you want to do this, because that affects what advice to give.
tell me how to make the web interface have a delay when the GPS device goes offline