@OceansEdge
That's correct, you need to increase your rest period by an amount at least equal to the amount of extension to your duty day.

You can have a split duty day up to 17 hours, where there is rest time in the middle that is double the duty time extension. For example, if you have 2 hours actual rest time(ie not including transfer time from the airport) in a suitable environment (eg hotel room) in the middle of the duty day, yo...