Never mind, figured it out. Since it was just a practice mission, I had the next waypoint after the 'Land' option as a 'Landing' waypoint back to the airbase. Apparently, it didn't like that so I added another standard waypoint between them and that fixed it. And by the way, the time 'On Land' is after the helicopter has physically landed. So 0:0:30/0 will leave the helo unit on the ground for 30 seconds before it takes off.