There are a lot of variables to consider here. Most people smoke ribs between 225 and 250º and many will cook their chicken quarters(or other pieces/whole) at higher temps. If you want to do everything at the 225-250º range, the chicken will probably take between 2.5 and 3 hours, or maybe longer depending on their size. Spare ribs take at least 6 hours and can take up to 8 depnding on pit temp and whether or not you foil them or not.
Bill