If you have requested that the mover provide packing services this will typically be done a day or two before the loading. The agent for the van line will contact you prior to this day and let you know what time they plan on arriving.
Be sure that the packers have ample room and a flat surface on which to work. Set aside and clearly mark items that you do not wish the movers to pack. They will not pack your basic necessities until the day of actual loading.
If you are moving alone we strongly suggest arranging for a friend or relative be with you. Another set of eyes and ears and just moral support will help you through the packing and loading process.