GameState::GetServerWorldTimeSeconds() is a network synced clock time. The server updates this value every 5 seconds to keep clients synced with a universal world time. Yet, clients values can differ greatly depending on their ping/jitter at the time of update. So it’s never truly accurate. Mainly an approximation.
I wouldn’t worry about time discrepancy on cool downs. If coded so the server maintains authority it won’t matter what the client does or doesn’t do.
Clients are always ahead of the server in respect to movement, location, actions etc. Inputs for an update interval are bundled and sent together. Meaning our clients execute them locally first (client-side prediction), then send bundled to the server.
Updates sent to the server are timestamped. Each input is timestamped. Packet headers have timestamps as well.