For a USB microscope, the practical approach is usually to record video, then combine frames afterward to simulate a long exposure. A true long exposure is normally one still image with the sensor integrating light over time, but many USB microscopes don’t offer that kind of manual exposure control.

A workable method is:

1. Record the microscope output as video or with screen-capture software.
2. Use a relatively low frame rate if possible to reduce the number of frames.
3. Extract frames and blend them into one image using a stack/average method.

In Photoshop, one example is loading the frames into a stack, converting to a Smart Object, and using a stack mode such as Mean. Similar stacking can also be automated with scripts or OpenCV-based tools.

So if your goal is a blurred motion/trail effect over 5 minutes, capture video first and merge the frames later. If you actually need a single true 5-minute exposure, that depends on whether the microscope’s own software supports manual long-exposure capture.