Method for operating a printing system for printing on sheets of a medium, the printing system including a printer with a medium input module and a finisher with a gathering station, the method comprising the steps of: a) providing a first print job including at least one set to be printed and a second print job including at least one set to be printed; b) printing all sets of the first print job; c) transporting the printed sets of the first print job to the gathering station of the finisher; d) processing the printed sets of the first print job by the finisher, finishing said processing at a first time point; e) determining a second time point at which the gathering station of the finisher will be ready to, or allowed to, receive a next set from the printer after the first time point, the next set being a first set of the second print job; f) providing a first-print-out time FPOT indicating how much time a sheet of the medium requires to arrive at the gathering station of the finisher after being separated from the medium input module; g) determining a third time point, between the first time point and the second time point, at which separating of the at least one sheet of the medium in step h) for printing of the next set has to be started such as to arrive at a predetermined time PDT at or after the second time point at the gathering station of the finisher, based on the provided first-print-out time FPOT; h) controlling the printing system to separate (S630, S680) at least one sheet of the medium from the medium input module at the third time point for printing thereon, the method characterized in that: i) providing a trigger time TRT indicating after how long of an idle time of the printer the printer is configured to commence a maintenance action; j) determining a fourth time point at which a sheet of the medium will be printed next; k) calculating a time between the first time point and the fourth time point; and l) comparing the calculated time with the provided trigger time TRT; wherein, when the provided trigger time TRT is shorter than the calculated time, in step h) the printing system is controlled to separate a sheet of the medium and to print a quality assurance sheet thereon before time equal to the provided trigger time TRT has passed after the first time point, and wherein the printed quality assurance sheet is transported to an output separate from the gathering station of the finisher. a) providing a first print job including at least one set to be printed and a second print job including at least one set to be printed; b) printing all sets of the first print job; c) transporting the printed sets of the first print job to the gathering station of the finisher; d) processing the printed sets of the first print job by the finisher, finishing said processing at a first time point; e) determining a second time point at which the gathering station of the finisher will be ready to, or allowed to, receive a next set from the printer after the first time point, the next set being a first set of the second print job; f) providing a first-print-out time FPOT indicating how much time a sheet of the medium requires to arrive at the gathering station of the finisher after being separated from the medium input module; g) determining a third time point, between the first time point and the second time point, at which separating of the at least one sheet of the medium in step h) for printing of the next set has to be started such as to arrive at a predetermined time PDT at or after the second time point at the gathering station of the finisher, based on the provided first-print-out time FPOT; h) controlling the printing system to separate (S630, S680) at least one sheet of the medium from the medium input module at the third time point for printing thereon, the method characterized in that: i) providing a trigger time TRT indicating after how long of an idle time of the printer the printer is configured to commence a maintenance action; j) determining a fourth time point at which a sheet of the medium will be printed next; k) calculating a time between the first time point and the fourth time point; and l) comparing the calculated time with the provided trigger time TRT; i) providing a trigger time TRT indicating after how long of an idle time of the printer the printer is configured to commence a maintenance action; j) determining a fourth time point at which a sheet of the medium will be printed next; k) calculating a time between the first time point and the fourth time point; and l) comparing the calculated time with the provided trigger time TRT; wherein, when the provided trigger time TRT is shorter than the calculated time, in step h) the printing system is controlled to separate a sheet of the medium and to print a quality assurance sheet thereon before time equal to the provided trigger time TRT has passed after the first time point, and wherein the printed quality assurance sheet is transported to an output separate from the gathering station of the finisher.