I'm not sure I've seen a post about this yet. Topcoder has posted their schedule for online rounds for TCO here: http://tco18.topcoder.com/algorithm/schedule/
It seems the round structure also seems to have changed. The rounds are 1A,1B, 2A,2B, 3A,3B, and a single round 4. Round 4 feeds directly into the onsite, with 14 finalists (and also 2 from a wildcard round, for a total of 16, 4 more from last year).
Another important information for some of you, the number of t-shirts increased to 400 (as opposed to last year 120).
Wow, they increased number of finalists, great!
Also note that rounds 1B and 3B start at an unusual time.