It has 3 "charges" every time you use it, 1 charge is used. It recharges everey 9 seconds. Aditionally the dodge buff stacks in time so when you use it while the buff is active you extend the buff time. So when you use all 3 after another(assuming you have enough rage) your dodge buff is ~18sek (minus global cds etc) and you have to wait 9 seconds (again minus global cds)to use it again.
If you pop it everytime it comes up you will eventually run out of charges where you can't use it at all for a little while. Generally not an issue because I'm busy using other abilities and it costs quite a lot of rage, but something to keep in mind.
For longer fights I try to pop it every 9 seconds. I like having the extra charges in case something goes wrong I can pop a few off in a row (as long as I get the rage though that is what berserk and incarn are for). For the 3 seconds of downtime I am planning on reforging haste and hit to mastery for as much armor as possible.