When the pregnancy is progressing towards its final stage the cervix starts to dilate which results in making the cervical entrance smoother and wider for the mucus plug to detach itself from its position and dislodge it into the vagina. Labor may start soon after losing your mucus plug, or it may take a few hours to days for the labor to begin. Some women often lose their mucus plug during the labor which comes out with blood referred by doctors as the bloody show.
Nature of the body, count of the baby and many hormonal factors play a key role in deciding the time of the labor to start. The time at which the labor begins differs from women to women as every labor is different. If you find any symptoms of labor like contractions which are painful or if your water broke or if you find more blood, after losing your mucus plug your going into your labor right away, if not it may take time for it.
Mucus plug in some women will not get dislodged until the labor and it gets detached during labor along with huge amounts of blood, this is known as bloody show which happens to few women. The time at which labor begins is not known and what causes the labor is also not known, one has to wait for the symptoms of labor after losing your mucus plug.