Definitely quite straightforward, and around 4 hours should see you up and back - depending, of course, on your fitness and the conditions, and how often you like to stop for taking photos, drinks/food etc. I'm always surprised at how long I stop, but I find the timings on WH are usually about right for me including stopping, but it's an impossible thing to judge as everyone's different.
There can be quite a lot of cornicing on the north eastern side near the summit, so if you're doing it later in winter or early spring, just bear that in mind.
I watched someone gaily taking a 'short cut' from the summit, across some cornices, a few years ago. He was clearly oblivious of the fact that there was technically nothing underneath him!
I can't remember how long it took doing both, but I'd reckon around 7 hours would be fairly average for most folk.