I have the same pressure cooker, and I had never used a pressure cooker before so I got quite frustrated when I first purchased it. You'll know it's come to pressure, because it'll beep (and the machine has the kind of beep that's hard to miss) and a 'P' will be at the start of the time, so if you had 8 minutes for example, the display would read "P8:00". You only get a certain amount of time for it to come to pressure before it gives up and goes into keep warm mode, then the only way I've figured out to get it to let you try to select the pressure mode again is to release the valve and try again. Maybe there's another way, but once I found this way worked, I didn't bother trying anything else...
What I normally do is use the browning mode to bring the liquid to a boil, shut the lid, then select high/low pressure mode and just watch it for a minute or two, then I kind of push down on the lid which makes the valve (not the dial thingy that you turn to release the pressure, but the silver thing above that that looks like a tyre valve of sorts) and that pops closed, then it beeps and the P appears shortly after. Again, I'm sure there's a better way, but this way works so it's just what I do.
Having said (all of) that, I've only really cooked casseroles and risotto's in mine so far, so I can't really speak from experience regarding why your rolled pork took so long, possibly because it was still frozen in the middle, but I would have just assumed, depending on how frozen it actually was, that it would only need a few minutes more. From what you've said though, it doesn't sound like it actually got to pressure.
