A fit(ish) rider can do the complete red loop in about an hour and a half with no hanging about, so 3 hours should see you around at a fairly relaxed pace. If you’re throwing in a descent of the Hope Line, then you might need to take a couple of shortcuts. It’s a figure of eight so that’s fairly easy.
As above, I’d recommend Long Way Down rather than Hully Gully for a beginner. The only other bits to watch out for on the red are a stone staircase at the end of ‘Homebaked’ on the lower loop on which panic-braking is not recommended, a section of steeper rooty stuff in ‘Bottoms’ and a couple of bits of the ‘Swoopy’ section which can catch you out, one with a bit of a drop to the side.