Is it possible to start prayer immediately after the Muezzin calls Allahu Akbar or just wait until he finishes the whole Azan? We work hard here in America and have just limited time for lunch and rest, just 45 minutes.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Performing the Prayer right after hearing the Athaan (call to prayer) is permissible, since the Athaan is actually to inform the people of the starting time of the Prayer. As long as the Muath-thin (caller to prayer) starts the Athaan, it means that the time of the prayer has started. But it is desirable to listen to the entire Athaan, to repeat it as the Muath-thin calls, to supplicate the Prophetic Du’aa' after it, to invoke blessings upon the Prophet and then, to perform the Sunnah prayer before the obligatory one. However, performing a prayer just after hearing the beginning of the Athaan is sufficient for the person.

Allah knows best.