Assalamu alaikum. If one's job does not permit him to go to the Masjid to pray (though he can hear the adhan without a speaker), is this a valid excuse for praying at home? He sometimes prays with his congregation when she can join him, but he prays by himself for a good amount of time.

Well, I do not know what type of job you have, and you mentioned "she," but who is she? In regards to this matter, there are different opinions: 1. Some say it is mandatory to go to the masjid. 2. Others say it is not mandatory. However, what is mandatory is that you pray in jama'ah. There is also a group of scholars who say it is a sunnah to pray in jama'ah, and this is a long debate. The majority of our mashayikh and ulama say you must pray in jama'ah, and if you are next to the masjid, then you pray in the masjid. An exception would be if your job is in security (for example, if you are a security guard guarding a specific place). Therefore, I say we need more information.