Muslims pray at dawn, midday, afternoon, sunset and night because God commanded prayer at fixed times, and it keeps a person connected to Him all day. Each prayer takes only a few minutes.
The fuller answer
The Quran says that prayer is prescribed for the believers at specific times. The five prayers are Fajr (dawn), Dhuhr (after midday), Asr (afternoon), Maghrib (just after sunset) and Isha (night). Before each, a Muslim washes (wudu), faces the Kaaba in Mecca and recites verses of the Quran, stands, bows and prostrates with the forehead on the ground.
Muslims see prayer as a break in a busy day to remember God, ask for guidance, thank Him and leave worries with Him. It also keeps people humble, because everyone stands in the same lines regardless of wealth and rank. You can find the prayer times for any city on this website.
And when you have completed the prayer, remember Allah standing, sitting, or [lying] on your sides. But when you become secure, re-establish [regular] prayer. Indeed, prayer has been decreed upon the believers a decree of specified times.
Recite, [O Muhammad], what has been revealed to you of the Book and establish prayer. Indeed, prayer prohibits immorality and wrongdoing, and the remembrance of Allah is greater. And Allah knows that which you do.
This answer follows the mainstream Sunni understanding and is general learning, not a fatwa. Where Muslims differ, the answer says so. Have a question of your own? Write to us.