Chalk works well on mats.
At a show, this can be done anytime after the judge has given final approval to the jump's position. Another way to speed up the change is to designate a steward specifically to the task. They should be briefed on how to place the boards and always adjust the broad jump first, then help with another obstacles. This approach also works well for the tire, table, and spread jump changes. A little friendly competition between stewards as to who can complete their task first can add both speed and fun.