In short, yes - as long as they still occur on the same days. For example, if you accidentally created an event for 8-11am, but meant to create instances for 8-11pm, you can easily change the time of all instances at once. Navigate to the Recurrence Masters page and click on the name of the master for which you'd like to adjust times. Click on Add Instances and recreate your instances exactly as you did before, this time choosing the correct times. Once you click Add, the system will overwrite the previous instances with the new ones, as the system allows only for one instance per day.