Like with getting a cube trough the green portal, just get yourself through. Set green portal 1 near the netted exit and enter it. Then set green portal 2 in the wall near the green gun.

Okay, but you can't shoot at the wall near the green gun because the grate blocks it.

The grate is not in the way of the green gun.

Ah yeah. See the problem with portal's "get the gun then use the gun" format is the players don't really understand how the gun works until they hold it in their hands, because it takes so much time to shoot portals at the right place that they don't experiment much. I and 2 other players thought that you simply couldn't walk through the time portals until I held the gun in my hand.

And the reason we thought that level 8 required box-grabbing is that we didn't see the black room to the left that is reachable with the box.

Puzzles shouldn't be lost because the players missed a secret room or didn't know how portals work. It can be hard to make things intuitive.

i had given up on attempting to go through the green portals till i read this post.

yeah it was hard for me to figure out the time portal as well. Because of portal 1 and 2 most people get a portal gun and know how to use it instantly because of how famous those games are. When you add a new type of portal and you dont explain it in the game, it can become very difficult for people to know what they can and cant do with it especially when they dont have it in their hands.