I am travelling from Dublin Ireland to London, on to Calgary & Vancouver , then on to Sanfransisco. I have been I need to leave about an hour to do customs clearance. But I fly out of Dublin at 6;30 am and was wondering if Customs clearance is open 24 hours? Also , if not, can I do it in Vancouver or San Francisco? I have done all other bookings , but am concerned I may not have enough time. My flight From London to Calgary also involves a stop (where i have to to take my case off and put on again) a 1hour 40 min stop in Toronto. Just wondering will that be enough time. It is all in Terminal 3 but i dont know how big this is. I am travelling alone. Excited but nervous of these things, aslo im used to booking my case online with Ryanair, but Air Canada and Alaskan airlines dont allow this - im presuming I am allowed do it at the airport - which is not the case with Ryanair where it would actually COST you more if you left it till the airport. Anyway, if anyone has any thoughts on any of the above questions Id be so grateful. Thanks in advance, Carmel

I don't know the specifics for your itinerary, but generally speaking, you go through immigration and customs upon entry to a new country. At some airports and for some destination, immigration and customs is done prior to departure. At any rate, customs and immigration will be open to process the passengers. So don't worry about that - if you need to go through immigration and customs, they will be open. As for checking luggage, yes, when you get to the airport, you can check your luggage. With a tight itinerary though, if you can go carry-on only, it's quicker.

By the way, that's a seriously round-about way to get from Dublin to SF. I hope you got an amazing fare.

I did not read it as a Dublin - London - Toronto - Calgary - Vancouver airports only, enroute to SF. I see mention of Vancouver and SF as red herrings. The way I read it they are flying from Dublin to Calgary, visiting Calgary for a while, then on to Vancouver to visit, then to SF, but I may be wrong.

Nonstop flights from Dublin to the US (mostly) have pre-clearance (immigration + customs) in Dublin.
OP's first flight will be from Dublin to London, though.
So, the procedures in DUB will be no different than on any other ROI-UK flight (regular security checkpoint).

We went through US immigration in Vancouver airport, fast and easy with our Global Entry when flying home to the US.