Be sure that the machine's page scanning capacity meets or exceeds your needs. Once the originals are scanned (or the print job is received by the device) most models in this class have job timers that let the operator know how long the job will take.
Another component on the input side of the equation is overall paper capacity. To maximize unattended operation during long-run print jobs, be sure the unit you choose has ample paper capacity. Most high-volume printer/copiers can be configured with up to five or six different paper supplies for a maximum capacity of at least 6,000 sheets. Be sure you also consider your common applications when evaluating paper capacity as it relates to different sizes, types and weights of paper. For instance, can the machine reliably handle a large job that requires copying or printing onto tabs or 110 lb. index?