Praise be to Allah.
The time of Maghrib prayer lasts from sunset until the red afterglow disappears; the time of ‘Ishaa’ prayer lasts from after the red afterglow has disappeared until midnight; the time of Fajr prayer lasts from the second dawn until sunrise. The evidence (daleel) for this is the hadeeth of ‘Abd-Allaah ibn ‘Amr ibn al-‘Aas in Saheeh Muslim in which this is mentioned. So long as the times of the prayers are distinct from one another, each prayer must be performed in its own time, even if the times are close together. Being patient in doing this is a kind of jihaad, and Allaah does not cause the reward of the one who does good to be lost.