Thanks Stephen but given your own great talent I'm not sure I deserve such kind words mate..
Yeah, I guess its all about practice and looking. It would be the same when you are drawing your sketches because although our respective end results are different, the process would be very similar. I have to admit that it can sometimes be a massive struggle to get the likeness right and after two days of fighting with a painting I often end up feeling like I've been waging war, not laying down paint..
How long?? Unfortunately, because of other business commitments I have, I can't paint continuously so it generally takes a lot longer than it should. That said, if I was lucky enough to be able to paint uninterrupted (and after the concept was client approved), it should take about 4-6 days to paint something like this from start to finish..