Is it preferable to delay the 'Ishā' prayer, and until what time, if I miss it due to the nature of my work?

Congregational prayer is an individual obligation upon free, adult men, unless there is a valid excuse.

If there is an excuse that permits abstaining from the congregation, such as the fear of losing or damaging property, then it is permissible to abstain. If there is no excuse, then it is not permissible to abstain.

It is not permissible to be negligent in performing the 'Isha prayer in congregation under the pretext that delaying it is better, because performing it in congregation is obligatory.

If 'Isha is missed due to an excuse, then delaying it until the first third of the night is recommended. What is after midnight is a time of necessity, and 'Isha should not be delayed until then except for an excuse. The optional time for 'Isha extends until midnight, and the time of necessity extends until just before dawn.

It is recommended to delay 'Isha for an individual and for the congregation—if it does not cause hardship to the congregants—until the first third or half of the night.