The timing for Fajr Namaz (dawn prayer) typically starts at the beginning of twilight and lasts until just before sunrise. For Islamabad, the Fajr prayer time generally falls between 4:30 AM and 5:00 AM.
For precise Fajr timings on a given day, you may want to consult a local Islamic calendar, a mosque, or a prayer time app. These sources can provide exact timings based on the date and your specific location.