Image forming system and sheet conveyance method

An image forming system comprising:

• an image forming apparatus to form images on sheets of recording media;
• a sheet processing apparatus including:
• a post-processing unit to perform a predetermined post-processing of the sheets output from the image forming apparatus on a processing tray, and
• a retaining channel disposed upstream from the processing tray in a sheet conveyance direction to accommodate at least a single sheet while the post-processing unit processes the sheets;
• and
• a controller operatively connected to the image forming apparatus and the sheet processing apparatus, the controller being configured such that the controller:
• calculates a target interval time between an interval start sheet and an interval end sheet among the sheets output from the image forming apparatus to the sheet processing apparatus based on at least one of sheet data transmitted from the image forming apparatus to the sheet processing apparatus and post-processing data transmitted from the image forming apparatus to the sheet processing apparatus;
• and
• adjusts an interval between discharge of the interval start sheet and the interval end sheet from the image forming apparatus to the sheet processing apparatus in accordance with the target interval time,
• stores at least the interval start sheet in the retaining channel while the processing tray is not available, wherein the interval end sheet by-passes the retaining channel.