My personal opinion. Yes. But having just started the ATPL ground its early days for me to give an informed opinion. Driving at the theory full time for a period of seven days is probably better than doing 3 hrs an evening after work, when you are tired, anyway. You'll also have the benefit of lots of clear head starts in the mornings.
I was susprised to discover a degree of overlap between PPL and ATPL theory. I expected the ATPL course to assume you had PPL knowledge - but it doesn't. For example, just a minute go I was studying how pressure instruments work just as I did for the PPL (more detail though at ATPL definately).
The PPL flying will also feed into the ATPL work in terms of providing a continuous flame of motivation. But make no mistake about the level of commitment you're taking on here and be careful not to overdo it and get demotivated and disheartened.