I'm having my first experience of last-minute-booking a Long Haul flight (LHR-DXB for this weekend) and have been keeping my eye on prices and ExpertFlyer.

I can see that there's still good availability in the current fare buckets, however I was wondering if at some point (e.g. t-72hrs) they close the cheaper fares automatically - whether officially or just by common anecdote?
I ask largely for interest's sake, but also because I was wondering if I should hurry up and book in the next 12-24hrs!

Thanks.