Guys, when you get a female's number, how much time after that do you call her? Ladies too, I need advice?

Yesterday, I was riding the bus, and I noticed this handsome guy kindof looking at me. I thought wouldn't it be great if we began talking, and kind of laughed at the thought of hooking up on the bus. To my surprise, he got off the same stop as I did and started speaking to me. He told me that he got off the bus just to speak to me and we had a lil conversation for a few blocks until I had to turn and go to my homegirl's house. He then asked if he could call me, I gave him my number. As we parted, I kind of heard him say something about calling me, but I couldn't hear when exactly he would. I wished I did a lot of things when I met him, such as get his number, but I was much too stunned. It is Sunday night I have not heard from him since, I met him Saturday afternoon. My question(s): What is usually a good time to call someone you spontaneously met? Is this normal? When should I give up if he still does not call? (I Can't stop thinking about him! It's almost like I imagined him!)