Most buses to the coast leave from the South Quito terminal, so that’s where you’ll want to go. You’ll want to find a bus to Pedernales and you’re correct in that it will take around 7 hours. Once in Pedernales find a bus headed to Canoa or Bahia de Caraquez and then tell the driver or bus attendant that you want to get off in Jama which is along the way. They’ll let you know when it’s time to get off.
One thing to note is that the community of Jama sits a little off the main highway so you’ll probably want to arrange transportation from the bus drop to where you’re staying beforehand. If you take the 7 hour bus ride to Pedernales, plus the additional hour or so to Jama it could be getting late in the day and taxis may not be plentiful.