You can change scheduled updates for one volume or qtree by editing the snapmirror.conf file on the destination.
systemA:vol0 systemA:vol1 - 0 23 * 1,3,5 systemA:vol1 systemB:vol6 - 0 23 * 1,3,5
The following example shows the changed update schedule
systemA:vol0 systemA:vol2 - 0 23 * 1,3,5 systemA:vol1 systemB:vol6 - 0 23 * 2,4,6