I only found this out today, mostly because I don't care that much, but there are new rules for the home run derby this year.
Round 1:
8 players, 4 advance, no bracket
Round is 3 minutes or 40 pitches and you get 1 timeout
Round 2:
Ranked 1-4 from previous round; 1 v 4 and 2 v 3
Round is 3 minutes or 40 pitches and you get 1 timeout
Finals:
Winners advance
Finals is 2 minutes or 27 pitches and 1 timeout
At the end of your time or pitch max, you get 3 bonus outs, home runs do not count as an out. A home run over 425 feet gets you a bonus out, but you only get one bonus out