When do summons arrive and question about failure to remain?

The reason I ask is because after talking to the police at the station, they told me I'd get it in a couple of days. They told me what I was recieving the summons for verbally. I'm worried because I was told they can add one more things to charge/ticket me for? Are verbal words enough? And because my paralegal or lawyer if I decide can't help me at all until it's received. Although the more time I. Have the better to start saving some money and learn about the laws (but what am I fighting?) One was a failure to remain at an accident. I knew the other party so I didn't see it as a big deal (at the time) to leave, grab my other vehicle and come back. I have text messages and pictures (iPhone so time stamped if that matters) to show that I returned about an hour later, with the drive being 20 minutes each direction. Does this make a difference? The police were no longer present but they had my plates, called me later that night, and I was at the station within 20 minutes of their call to explain and get told what was going to happen. I had NO idea how bad a failure to remain was. My license is fairly clean, one 10 over ticket and that's it. I don't know if collisions count, but I had one at fault like 2 years ago. Thanks.