New Grad RN Had Interview and Needs Advice/Suggestions PLS

I had two interviews recently. One on L/D and one on a postpartum unit. The interviewer for L/D said they would have a decision by the end of this week. This is also my first choice in hospital and unit. The interviewer on PP stated that she would have a decision made soon (possible today or the following day) since she wants to fill the position quickly. The interview went really well and she seemed very interested.

If postpartum calls me back w/ an offer I want to be honest and ask her if it would be okay to have until the end of the week to make a definitive decision, but what if she says she needs a decision right away? Is it okay to state I'm waiting to hear back from someone else so I can weigh my options or should I accept the position and if L/D calls me back, later decline the Postpartum offer since I would not be starting hospital orientation for a couple of weeks. I know she wanted to make a decision right away because she wanted the background check to process before the next orientation date.

Any advice would be great. I hope my posting makes sense. It's complicated. Thanks.