Putty

Hello, I've been working on a mission for my group that I play with that utilises Zeus much like the MCC sandbox. However, I have come across the problem that people can only load into the mission if they join before the mission is initiated. This is a huge issue as it means that for Zeus to set up a mission, everyone needs to be already connected and it is impossible to connect if the mission is already ongoing. I've looked around a bit and still haven't found an answer. Any help will be greatly appreciated :)