Here is the post:
https://www.reddit.com/r/TheSilphRoad/comments/74glq3/the_art_of_synchronization_an_ultimate_teamwork/
When you back out of the gym fight then start fighting again, you do not rejoin the same players that were already fighting. The game creates a new instance for everyone that left. The closer in time that different instances finish, the less time there is for the defending team to feed berries in between. If you can finish three instances at the same time, it will kick the defender no matter how much it is being fed. You then have 10 minutes to repeat with the next 5 pokemon before the defending team can add new pokemon.
Group of players start a fight. (instance 1)
Some back out, then start again. (instance 2)
Out of the second group, some back out, then start again. (instance 3)
If the defenders are only feeding when motivation drops to 1/3, then you can do one normal fight, then create two instances and finish at the same time to kick the defender. If they are feeding golden razzberries after each fight to keep motivation full, then you need to finish three instances at the same time.
Anyone new starting a fight will go into instance 1. After that instance is finished, then new players will go into instance 2. If there are uncoordinated players also fighting, that can speed up the time on instance 1. I saw one suggestion in that case that you might want to create a further instance 4, leave one player in instance 1 but not attacking to give the other players time to leave and re-enter into instances 2-4 so they can all finish at the same time.