@ Pyo: LOL DT level 1 and 2 are overall balanced. I think lvl3 is a bit OP though. I know if you place a new DT the old one disapears, don't know how potion of focus effects it though.
CD for the ulti is too long to make one, wait for CD and then another one.
First one disappears before the CD for DT is finished.
Potion of Focus or whatever the name is allows you to use your spells once again, no matter what CD of whichever spell you have.