While experiments have been run online for some time with positive results, there are still outstanding questions about the kinds of tasks that can be successfully deployed to remotely situated online participants. Some short tasks, such as menu selection, have produced viable results but these do not represent the gamut of tasks that interest human-computer interaction researchers. In particular, we wondered whether long-lasting, time-sensitive tasks that require continuous concentration could work successfully online, given the confounding effects that might accompany the online deployment of such a task. We ran an archetypal interruption experiment online and in the lab to investigate whether studies that are long-lasting and timesensitive might be more vulnerable to a loss of control than the short, time-insensitive studies that are representative of the majority of previous online studies. Statistical comparisons showed no evidence of performance differences across a number of dimensions. Despite these results, there were issues with data quality that stemmed from participants misunderstanding the task. Our findings suggest that long-lasting experiments using time-sensitive performance measures can be run online but that care must be taken when introducing participants to experimental procedures.