It is possible to find a time slot as to where this second job begins and ends. But then we'll have to start defining the timing of one who works "night and day". Which can be quite repetitive and somewhat nitpicky.
For example, if we define "night and day" as what Michael mentioned in Workin' Day and Night, and that is, from sun up to midnight. Over here, sun up is around 6:30am, so that means working from 6:30am to 12:00am. That's 17 and a half hours of work for the first job. In which case, we could assume this second job is somewhat small, and perhaps, requires only an hour or so, after the initial job.
Given that the next line is, "She waits her life away", one could also assume that both of her jobs are that of a waitress. So, another way to look at things is that she has two seperate waitress jobs in the same restaurant. Whether that's possible, I'm not sure. If it is, then perhaps, both jobs share the 17 and a half hours of work.
But if it's not possible to have two seperate jobs as a waitress in the same restaurant, and one of her waitress jobs requires working from 6:30am to 12:00am, I do wonder if there are any restaurants (or any other job setting that require waitresses) that are open from 1am to 6am... Do note, this is in total disregard for the needs of rest.
There is another point that perhaps, the second job could be so trivial, that the singer completely disregards it when he sings, "She waits her life away". At which point, the first suggestion could still work.
Whatever the case, this seems to be too much of a nitpicky sort of argument for my liking, so maybe I'll just stop right here.