Project Browser Thumbnail Refresh?

Thanks, those settings may come in handy later, but for now it isn’t so important that I must start creating specific thumbnails for each project. I just want to (somehow) refresh Project Browser images so they reflect most recent project startup view.

Some thumbnails do seem to change from time to time. Some are more up-to-date than others. However, I don’t know what condition triggers this update. I would like to know so I can do it manually for a quick refresh.