When planet scanning, zoom outs and ins can take a fair bit of time. Instead, hit the left mouse button to focus on a planet. Keep the mouse cursor over the planet you selected, then hit R to scan. Move the camera, find another unscanned planet, then left-click on it to zoom directly to that planet. Lather, rinse, repeat until all are scanned.

If you hit R when your mouse cursor is over another planet, the map will zoom out, then in to that other planet, taking valuable time that you don’t have. ;)