CLimb up Llanberis took me 2.5 hours of spinning and carrying, with a bunch of lads and a spot of competitive nonsense – I’d budget another hour for someone not used to carrying a bike. Be careful how you come back down – the Ranger’s path would be a leap up for a trail centre rider, as it’s rocky, the ground moves about underneath you, and there’s lots of rocks and no soft landings.
Coming back down the way you climb would be better – slower, more people (so more stops) and less face-puncturing opportunities. I intend your missus no disservice, btw – if she wants to shred down the thing like Racehl Atherton, I apologise.