This is an old question, but perhaps some people are in the same position, so...
I've just come through my viva - in computer science in the UK. I had a lot of the same anxieties, but I did know that in the viva they were checking:
whether it was clear that I understood what I had done and why I had done it
whether I could justify my work's novelty - not that it was somehow ground-breaking, but that it explored a specific avenue that hadn't already been investigated and reported
whether my thesis made sense, i.e. were the experiments relevant, fair, well reported and analysed, and was the story told reasonably well from motivation through to related work, analysis, and conclusion
was it a significant contribution to the field
I guess it's that last one that was bothering the poster. The examiners didn't care about the time spent, just whether the work was substantial enough to make it more than "just" a Masters level piece of work. That judgement could be on the scope of the work, on the novelty, on the thoroughness of the analysis, but never on the number of hours spent on it - they didn't ask and I don't think they care.
As others have said, the PhD programme is in a way distinct from the PhD thesis. In those 3+ years you're supposed to be apprenticed into academia, learning skills, developing networks, trying your hand in submitting and reviewing work at various levels, etc. This programme is tested indirectly in the thesis and the oral defence in the sense that if the journey has been successful then your work is of a certain quality (not exceptional, world-beating, just good enough to be of interest to the relevant research community).
In either case, once it's submitted there not much you can do about the thesis, but in preparation for the viva you can ensure you've re-read your work thoroughly (warning, you may spot mistakes afresh) and that you can justify your decisions and omissions. There are useful lists out there with common viva questions, but they can be quite overwhelming especially if you don't have loads of time to prepare.
I was given the opportunity to kick off the viva with a 10 minute presentation setting out the motivation and chief contributions - this was a nice way to remind myself and the examiners of the big picture. This might be a good preparation activity even if you don't actually present it on the day.