To make connections with an international flight - I would book the earlier flight - just to give you more time and leeway in getting from Vegas to LA.

What's the difference really between a 4:30 am wakeup call or a 3:30 am wakeup call/alarm clock?

You can always nap later in LA, where - since you arrived early - you will probably sail through baggage check and security without any problem.

Actually - have you looked into staying at a hotel overnight by LAX? There are a number of reasonably priced places and then you don't have to worry about getting to the airport with time to spare. http://traveltips.usatoday.com/hotels-near-lax-airport-shuttle-36697.html

Are you saying that you are unable to check your luggage through? Why is that?

Are you sure you're not transferring from T5 to T7? Are you connecting from Delta to United? You should be able to through check bags and that should be sufficient time but if you're traveling on separate tickets and can change to an earlier flight, you may want to do it for peace of mind.

You probably could make it, but if an earlier flight is available, then do it. You will have time to check in, relax and have a cocktail.

You've got three hours to get off the first plane, go retrieve your luggage, get luggage to Delta (is it Delta at Terminal 5?) to check in and get to the second terminal.

For me, that would be more than sufficient time, but there are other factors which you may want to consider, such as how many pieces of luggage, whether one has mobility issues and needs help around the airport, etc, that may require more time; so

if a three hour window at night - when the airport traffic tends to die down a bit - makes you feel uncomfortable, then by all means book an earlier flight.

We left Vegas at 17:01 and arrived LAX at 18:15 flying UA. We had to collect our baggage, catch a bus to another Terminal, walk to Qantas section, check in luggage, go through security and then wait for flight back to Brisbane at 23.45. We had time to have something to eat then sit for a fair while waiting to board. We had 2hrs more than you will though. You could probably do it but are both legs on the one ticket? I was told to have those last two legs on the one ticket so that if anything happened with flight cancellations/delays on the Vegas to LA flight Qantas were obliged to get us back to Australia on another flight. I played it safe and booked us on a flight that gave plenty of time between arrival and departure. You would probably have time but there were a couple of airlines leaving late at night so it was quite busy at security in the terminal (and the bar).

If these are two separate tickets, then I would not chance it. If it's the same ticket, you'll probably be able to check your bags through and it should be no problem.

I made a similar transfer at LAX a year ago from JetBlue to V Australia and had time to spare. I think my time between flights was 2 hours. I walked from one terminal to the next.

Having said that, I was doing this a bit later in the evening. I think you'll find it to be much busier around 7pm, and that might make security lines significantly longer.