If the time for Asr prayer starts at 0305 pm, can I pray in my office, in a small group, after that time even if Azan has not been given in the local Masjid?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions. If you are certain that the time of the prayer has entered, you can pray regardless of whether the Muezzin has called the Azan or not. People can pray in congregation without being in a mosque. But performing prayer in the mosque is better and the more the congregation is big the better the reward will be. All the four schools of Fiqh are agreed upon the above. Allah knows best.