Hunter Paces are typically W/T/C and no more then a few miles. If your horse is in normal trail condition, he'll do fine.
My normal rule of thumb when I used to compete was to trot up hills, walk down hills, and trot/jog the flats. The last time I competed (many years ago) my team came within 3 seconds of the ideal - really a matter of luck rather then skill for the most part.