According to wowhead and with my own anecdotal experience to back it up the 4 set will never reset blade dance under 3 seconds remaining.
This seems like a stupid limitation that actually slows you down for getting more haste. During pulls the first 40 seconds my CD for blade dance is like 3.5 seconds so I have like one shot to get a reset or I just have to wait.
Why is it like this blizzard?