Contractions @ 34 weeks

Monday, when I was urinating I noticed blood on the tissue but not in my urine & it was very light. So I waited til tuesday morning to call my doctor because it was so late. Once I told the MA what was happening she kept telling me they will give me a call back & I never got a call back that day before they closed. So I decided to go to the hospital that same night & they had this strap around my belly to listen for baby heartbeat. They told me she was doing very good but they noticed I was having contractions. I was there probably a hour when they told me I had 4 contractions. I didnt feel a thing. They checked me vaginally & there was no bleeding so they said I dont have to be on bed rest due to the contractions cause there's no bleeding. They told me I was good to go but im curious.. Even though the contractions are very light cause I dont feel them, how long after does someone go into labor after contractions started? (Your personal experience, not in general)