Originally Posted by CarolineW

I am taking a flight out of YVR to the US around 8 am, on a weekday. Will the US immigration and customs pre-clearance be open at that time (i.e. 5-6 am), so I can clear it there ? Or they only open later on ?

I am rather fearful of being cleared within the US and then missing my onward flight... clearing in YVR is definitely much better.