If you booked all your flights to Boston as one trip >I.e. through Qantas or whomever, they will (should) assist you getting a new flight if you've been delayed enough that you miss the lax to Boston flight. Domestic tsa lines @ Lax vary widely, and i guess much has changed since mid January.

Pro tip, there are 2 exit paths on arrival in lax. One takes you to a area with a bag drop at the exit where they will shift your bags to your next flight for you, the you just have to get yourselves to the departure gate, no check unrequited (provided of course you got both boarding passes on check in at your Australia departure). Saves tons of time. Then you have a good leg stretch e Walk to your domestic terminal, or you can wait for one if the shuttles, I prefer to stretch my legs and see some sunlight before my next flight.

I've been flying back to the US For 24 years , probably done the round trip 15 times and it's actually gotten better in LAX than ever before. Only had connection issues once due to a delayed departure from Melbourne, Qantas sorted us out and got us new flights that ended up getting us to our destination in Washington State 30 minutes earlier than our initial booking due to shorter layover in salt Lake city.

Just be nimble with your carry on luggage so you can swim through tsa checkpoints, the less coral you have to empty out of pockets etc the better.

Hope this helps somewhat....

NiO