Timer In Audacity At Bottom Of Screen

I record a Podcast each week then publish it after editing it. My issue and question revolves around the timer at the bottom of the screen. My podcast is 30 minutes. However, I normally record longer than that then go back and edit the podcast down to the 30 minutes. Is there a way on the timer that it can be set with the total amount of time I used for a particular recording so that it will count down backwards as I edit things out? It would help to know how much more time I need to delete in order to get to my allotted time of 30 minutes.

Thanks for any help you can share with me.