Don’t assume to know why he may have called 12 hours later or three days later. He may have waited three days because he was nervous, busy, at work, misplaced your phone number for a few days, had a family reunion that week. The possibilities are endless. What you need to focus on is whether or not he took the initiative to make contact with you.
Finally, I have heard women say that if a guy doesn’t try to call at least two or three times than he is not really interested. This is one of the craziest things I have ever heard.
Even the most confident guys out there are not going to repeated call a woman they just met who does not have the courtesy to return their phone calls. Not returning a guy’s phone call sends the clear message that you are not interested in him, and he will move on.
The easiest way to tell if a guy is interested in you is if he intentionally tries to contact you; whether that is through text message, phone call, or sending flowers. He is taking time out of his day, even if it is just a few seconds, to contact you.