I know that if there is no delay in waypoints, it will be a fast waypoint. In this case, will there be a problem when going to the 6th waypoint. (Normally, the 4th and 6th waypoints will be adjacent, to open the servo exactly in place)
4. Do I have to add a 1 second delay to the waypoint?
If your concern is hitting the waypoint precisely, you might set ATC_DECEL_MAX to a low enough value that your copter slows as it approaches the WP. This will affect all waypoints.