How many prayers in a day in Islam?

At least five obligatory.

The timings vary from day to day and place to place. However, the Muslim prayer timings are calculated from the movement of the sun round the year. Fajr prayer is offered during real dawn till sunrise. Zuhr in the beginning of afternoon when the sun declines a little till the shadows grow twice the size of the objects. Asr prayer form that time till sunset. Maghrib from sunset till almost 1 hour and twenty minutes after sunset. After that Isha prayer till after mid-night. Tahajjad prayer after Isha prayer till real dawn.