Extra Legroom Seats: How early should we get to LAX & LHR?

Hey All - what an amazing source of knowledge this board is! Thought I would use the groupmind to see how early we should get to LAX to try and get 3 extra legroom seats together. I've already paid for the seats, I'd just like to be able to sit with my husband and daughter during the flight. I'm also hoping that if we get in the row of 4 that we'll luck out and not get anyone sitting in the fourth seat
So, what say you all?
Also - one bonus question. While we leave on a Friday, we land on Saturday - my birthday! How hard will it be to try and get a glass of bubbly back to Economy? It's for medicinal purposes - really!

So, what say you all?
Also - one bonus question. While we leave on a Friday, we land on Saturday - my birthday! How hard will it be to try and get a glass of bubbly back to Economy? It's for medicinal purposes - really!