hey i see people moving right after they fire cero like the beam doesn't even fully extent and they start to move . Its like they move while the cero is firing, is this a bug?

Ya ,mainly caused by the lag or flash step.

yea and i thought cero was supposed to have like a 3 sec delay and people fire and move like in 1 sec

Lag and Stuff my butt, I used Cero with the server running full force and I moved. The Same happens with Hitsugaya's Shikai. The dragon's STILL extending, and they just step aside. A LOT of abilities have this bug.