You can zoom in or out in the Pixel Editor's sequencing grid:
Zoom In
To zoom in, click the zoom in icon. Or you can drag your mouse across the yellow timeline (and waveform if displayed) and the grid will zoom into the selected region. .
Zoom Out
To zoom out, click the zoom out icon, or right-click on the yellow timeline or waveform. You can also zoom out to the default level (15 seconds) by clicking the mouse wheel while cursor is in the timeline/waveform area.