Alla prima - a rod for my back?

Hiya all, As someone who is mostly forced into being as a Sunday afternoon painter by work & how hot/cold the conservatory is, I've come to a dilemma. I love to start & finish a painting in one go if possible. I believe it makes for a fresher look, plus I can't mix the same colour twice! My last effort took 6 hours straight & left me somewhat drained, even though I was enjoying it at the time. Many artists pick up & put down their work for days, weeks, months or even years, apparently. I suppose I should try it, but can't help thinking that the work would look like a kit of parts rather than a flowing painting. I don't have the luxury of leaving my kit out when I finish up, but I can find the odd hour or two in the evenings sometimes. Unfortunately retirement isn't an option yet, but would help a lot.