Ok, so it sounds like the request is to have the (skid steering?) vehicle turn off all its motor (i.e. set motor outputs to SERVOx_TRIM) just like Hold mode does… but just for a specified period of time and then it should continue with the next mission command.
So the manual method of doing this would be to change the vehicle into Hold mode either from the transmitter or by sending a SET_MODE command from mavros. According to the AP ROS wiki page it looks like, “rosrun mavros mavsys mode -c 4” would switch it into Hold mode. And then later the vehicle could be switched back in Auto mode and it would continue with the mission.
Perhaps a better approach would be for us to add support for Hold-within-Auto. I.e. a mission command that simply shuts off the motors. That’s not very hard but we need to decide which mission command to use (list of existing commands starts here) or maybe we need to create a new one.
At the risk of being a bit pedantic, Hold-within-Auto is actually quite different than using DO_SET_MODE because if we added support for DO_SET_MODE then the vehicle would switch out of Auto into the Hold flight mode. We don’t process mission commands in any mode besides Auto so the vehicle wouldn’t move onto the next command after the NAV_DELAY completed.