Disagree - maybe some can - and be very effective - others not so much. And yes, I have been bi-vo with a full time job - including when I was in the Army.
The trick is to make good use of the time. Sure some jobs you can study while on the job - ie security guard - others not so much.
But first a 40 hour job may take up to 50 hours when you consider travel time and lunch. If you only have Sun AM and Wed PM - that would be a bare minimum of 5-10 hours of study. You need a bare minimum of 5 hours sleep per night - figure 5 hours for church attendance. Of course other meals - figure about 45 minutes per meal, lets say 15 hours a week for required work around the house,
That leaves 26 hours a week for visitation, counseling, administration, other church activities, hospital visit, other meetings and not to mention family time.
Can it be done, yes - but everyone is not able.