Trim now or do major cutting while dormant? Pecan trees, North Texas

Client is insisting that all of the smaller branches hanging lower than 7' on these pecan trees be trimmed now. I'm trying to tell him that in order to pose the least risk to the life of these trees, we need to wait until the tree goes dormant and cut some major length off of these absurdly long limbs as it's only a matter of time until they start falling off and splitting the sides of the trees open, ultimately killing them; and that doing smaller trimming would be both a waste of time and double the stress on the health of these trees. Any advice for this situation?