Thanks for everybody for your kind replies. For my mind, the written phrase bears two meanings. The correct one could have been understood only from intonation whith which Atkins had pronounced it. If the stress was on the "all", the meaning could be "I have played it off, all my dity, job, all my life and hello heavens". If it were on the "in a day's work", it might have been just simply as "it's my work to earn money, and no fanfares are required".

"It's all in a day's work" means "It's my job" or "It's what I normally do anyway" or "It's no big deal!"

It’s all in a day’s work" > it is just part of my work that I do (everyday)

Yes, James. Now I got it. So, "it's all, and I've done it out, and out of debts of my Earthy duty" - right?

Actually not quite: Atkins isn't saying 'it's his duty' he's actually down playing how big a deal his work for the army was. Similar points but different, it encaptures how he acknowledges that his life has come to an end; he has accepted his fate and in quite a casual way he dismisses how big a deal his work and death is, and almost says 'it's nothing'.