This guide lists the changes made to the original route found here- http://www.speedrun.com/DiRT_3/guide/stuwz Some DNF skips may require difficulty switching and/or favourable rng. Refer to this guide here for details on DNF skip- http://www.speedrun.com/DiRT_3/guide/uy58e
Minutes saved is only an approximation based on my own rough testing.
Season 2-
Winter Forest Classic -> Oakley Superstars: 3-4 minutes saved
Season 3-
Colorado Buggy Bash -> Ostlandet Cup (S3 DNF Skip, 2nd place is fine): 1 minute saved
Battle of the Buggies -> Riveria Open: 0.5 minutes saved
Season 4-
Snowmass Takedown -> Le Seuil Legends (S1 DNF skip): 2.5 minutes saved
Lake Superior Showdown -> Safari Sprint (S1 DNF Skip): 2.5 minutes saved
¤Note: If both of the above DNF skips result in 2nd place then you will be below the total points necessary to unlock the finals. There is only a buffer of one 2nd place. In the case that both are 2nd place, either replay one of the tracks or for safety play Oppland Classic (S3 DNF skip) to make up the missing 10 points for a time loss of around 8.5 minutes.
Landrush Open -> Monster Superstars: 2 minutes saved
Ultimate Rally -> Ultimate Rally (S4 DNF Skip): 2.5 minutes saved
Ultimate Landrush -> Ultimate Trailblazer (S1 DNF Skip): 2 minutes saved