Wait until the coals are white hot with no smoke and then move them inside of the tent. I don't know how long to tell you to wait after the coals are inside the tent. Anything at this point would be a guess. I'd wait every bit of a half hour to 45 minutes myself. Before doing any of that, I'd practice getting into and out of the tent as quickly as you can, securing the flap behind you once you get in. The CO won't drop as much as you think, but you'll lose some CO. It may be beneficial to place a tarp over the tent to help contain the CO, including reducing the amount lost through opeing up the flap to get in. That's why it's best to start with a CO level as high as you can get it. I hope you plan on using enough charcoal. Honestly, this is why a CO meter is so beneficial, as you can do some "dry runs" and make sure the level is getting high enough, how much it drops when the flap is opened for a few seconds, that kind of thing. This is not a good method to screw up, as you can be left in a very bad way if you fail with it.