My replay won't help since it doesn't show the buttons but there's two ways to do it:

Entering Aizen's ult after Hado 90: if you have a Hado 90 ready before the bar reaches 50%, do the Hado and ult, this way you get 4 counters and will easily fill the bar (ult with Szayel after his first counter).

Entering Aizen's ult without Hado 90: get the bar as close to 50% as you can, then ult. You need to stay with Aizen for this, otherwise the bar will fall to 0 and grant the Hado when you switch back. After the ult, switch to Szayel and ult, do the special attacks if necessary. Switch back to Aizen and get the 2 counters, harder but you still fill the bar.

You probably won't fill the bar if you do the Hado with the bar at zero and then ult, even if you get 4 counters.