Is there a limit to the duration of swishing with chlorhexidine oral rinse?

With solutions like salt water that are innocuous, if swishing with it for 30 seconds is beneficial, it seems that using it longer would be even more beneficial.

But for prescribed oral solutions like Paroex (chlorhexidine gluconate), where the instructions states to swish for 60 seconds, is there any harm or benefit in swishing it for longer than 60 seconds?