[NiteWave]

Wonder how long it can shut down the instance, what the settings responsible for it.

lsws admin console->Server->General->Graceful Restart Timeout (secs):
"Graceful Restart Timeout During graceful restart, the new server instance is up, while the old instance will continue to handle existing requests. This timeout defines how long the previous instance shall wait before exit. Default value is 300 seconds, -1 means wait forever, 0 means no wait and abort immediately. "