I have an 8 team set up for 5 games guaranteed over three days (20 games in all), with two divisions and four teams playing a 3-game round robin followed by a two-game playoff with top four teams from round robin seeded in the Winners' bracket playing for spots 1-4 (and an analogous set up for the Loser's bracket).
Assuming you start Friday a.m. you can finish it all in 2 1/2 days. You need to have two fields and 10+ hours of daylight, or stadium lights and play 1-2 games at night to fit this in by lunch time on Sunday.
Let me know if this is of interest and I'll email you the set-up I used this past Thanksgiving at the 4th Annual Singapore Baseball Classic (a.k.a. "Turkey Tournament").