Promotion

I am getting a promotion at work soon. The person I am replacing is not going to be here and it’s going to be a gap for two weeks until we hire a new employee. What do I do? Do I stard doing what the person who already left did or carry on doing my job for another two weeks until I am officially told that I am in charge of that position?
I wasn’t given an official date yet. They are not going to hire anyone temporary. They know about the gap. I think I can handle both positions.
Thanks
wikipedia.org - Promotion(marketing)