The present study explored how deviations from the expected time point of a secondary task affect dual task performance. In two psychological refractory period experiments, participants responded to two tasks separated by either a short or long delay. In contrast to traditional dual tasking studies, however, the identity of the first task probabilistically predicted the delay at which the second task would occur. Violations of these expectations impaired Task 2 as well as Task 1 performance. For Task 1, this effect was more pronounced when Task 2 occurred earlier than expected, while for Task 1, it was more pronounced when Task 2 occurred later than expected. The data pattern is consistent with the idea that sharing of processing resources can be proactively scheduled (i.e., based on early available Task 1 features) and re-allocated when predictions are violated.