Job interviewer told me to call them in a day??

So I originally applied for a server position at a large casino being my resume has supervisor/management experience they called me in for an interview to be a manager and oversee operations for the shops inside the casino. They told me all the info on hours, salary, what the job would be like etc. at the end I was going into the conversation of when would the position start? And the interviewer said why don’t I give it a day and contact him if I truly want the position. I am a little confused on why they would say that and would have liked to accept and offer right there 😅 I also want to be able to negotiate my salary and don’t know how I would do that over the phone after accepting the position. Hmmm are they really just thinking about if I’m the right fit lol