International flight landing at LAX at 12:50 and departing on a separate domestic ticket at 16:30. Is that enough time to go through immigration, security, luggage, etc?
Arrival via Singapore and departing via United. I am unsure of the terminals. Late September.
In your case, you'll be arriving at TBIT and have to check-in for your next flight at Terminal 7.
The check-in deadline for United domestic flights at LAX seems to be at 45 minutes before scheduled departure, so 15:45.
This means you have 2h55 to:
After that you will still have to go through security and to your gate before it closes.
If all goes well, this is most definitely doable (should probably take about 1h-1h30, though it depends a lot on where you are seated on the incoming flight, whether you can use the APC kiosks, whether you have status and can skip queues...). However, if there are any issues, remember that if you miss any of the deadlines for the second flight, you will be considered a no-show, and your ticket is likely to be cancelled (along with further segments on the same ticket, like a return flight). In that case, you have to book and pay for a new flight at your own expense, at last minute prices.
United does not have an official "flat tire policy". They say that they will "generally" rebook people who arrive within 30 minutes on to the next flight, but you can't count on it.
Depending on your final destination, the 16:30 may also be the last flight of the day. In that case you may need to rebook on a different airline, or pay for a hotel, as well as transfers to/from there, meals, etc.
Here you have probably about 1h30 of buffer. We can't decide for you whether you think that's enough.
