Fajr is prayed from dawn until sunrise; Dhuhr from just after midday until the afternoon; Asr in the late afternoon until sunset; Maghrib just after sunset; and Isha from nightfall until midnight (and, in need, until dawn). Their appointed times are established in the Quran and Sunnah.
References
Quran 4:103Sahih Muslim 612
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.