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 Templates page and click on the name of the template 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 the Add button at the top of the page, the system will overwrite the previous times with the new ones, since the system allows only for one instance per day.  

This does not completely overwrite the instances, it only changes the times.  If someone was already registered for one of the instances, they'd be still registered.