I just did a google on it, it says that you switch parties regularly up until around Chapter 9. Chapter 11 is when the game is supposed to open up and people say it's about 25 hours into it. So it takes a long time to stop changing parties up.. ugh.
“Anna, my strong, terrifying Anna.” -Cas
"You lack the requisite spine and testicular fortitude to study under me" -Elodin