Lskravy

I'm heading out on a British Isles cruise in July and staying in London the night before the cruise. My plan is to take National Express from LHR to Victoria Station (where we are staying). My question is how long do you think it will take to get from plane landed to wherever we need to get on the bus? It has been quite some time since I've been to LHR, but last time it took 2-3 hours from what I can remember. I would like to pre-book my National Express tickets. Thank you 🙂