In a mix effect, the T-Bar and associated controls match the main Switcher. The drop-down Duration menu in the footer of the pop-up effect bin offers several convenient presets.
It’s different in an M/E displaying a compositing effect (such as the Default > 4 Layer effect), however. In this mode, dragging the T-bar vertically adjusts the virtual camera distance for the active effect between 100% and 400%. (Timing controls for virtual camera move are located in the footer of the Comp bin.)
Tip: The maximum duration for an animated zoom is 30 seconds.