No, the number appearing in top left in the "H" box is the time per division setting, NOT the time it takes for the whole screen. If you had "20 sec" here, then the whole screen takes 12 x 20 sec or 240 seconds. So no wonder you had to wait. Note also where I have the trigger set, near the leftmost edge of the screen, not in center.
I don't think I even know where the force button is. Never used it in my life.
It's the bottom rightmost button on the DS1054z panel.
It's pretty important on the DS1054Z because the key sequence (trigger) MENU-MENU-FORCE-MENU, very fast, followed by Utility>System>System Info, is how you get to the full System Information screen where all the software and firmware are listed, plus startup count and time in use.
You can also use it to force a trigger in Single Shot mode...