Some parts of the Llanberis path have been smoothed so it will be a little quicker than it used to be. If you budget for three hours all done, I reckon that might be about right. I take it you’re doing Ranger’s down?
Given mixed ability some of you might be a bit boogered after that, so don’t forget there’s the run down the slate mines option on the other side of Llanberis. You could have breakfast/lunch at Brynrefail and then ascend from there or go down towards Nant Peris and ascend most of the way you’ll come down (you’ll have to head towards Mynydd Llandygai and turn right up to the mines for the top [and steepest] parts). If that looks a little short, you could also fit a loop in of Moel y Ci in and go into the woods for the jumps, drops and berms.