Or HaChaim on Exodus 18:22/אור החיים על שמות י״ח:כ״ב

1 בכל עת, "at all times." The Torah hints that even at times when Moses was busy receiving instructions from G'd these judges would continue to dispense justice, something that Moses had not been able to do.

2והקל מעליך ונשאו אתך, "so they shall make it easier for you and bear the burden with you." Yitro meant that his suggestion was intended to lighten Moses' burden, not that he would not be allowed to judge any other than the most difficult cases. The idea was that the other judges should share the burden together with Moses.