Recent studies reported that central processing duration influences processing order of two tasks in the psychological refractory period (PRP) paradigm. This study examined whether the duration of response execution influences the processing of task order. For this purpose, a tone discrimination task was combined with a letter discrimination task. Both tasks were presented in random order using different stimulus onset asynchronies (SOAs). In one condition, participants responded to each stimulus with a single key press (easy response condition). In the other condition, the tone task required a single key press, whereas the letter task required a more time-consuming key press-sequence (hard response condition). The results showed that participants tend to perform the tone task first more often when the response requirement for the letter task is hard, rather than easy. This result is consistent with the notion that participants optimize response scheduling in dual-task situations.