Party-There should be a square indicating a party is going on; orange bar if the party is about to start counting down from 15 mins or a red bar if the party has already started, counting down the time left for the party your club is doing. You can tap on that square and start doing actions (snark, rave, sigh, lecture); alternatively you can go to your club home page, there should be a green button that says Join Party! provided the party has started already. If it's still within the 15 minute wait time, it'll be grayed out and you'll need to wait until the party starts to join.
PDT-Pacific Daylight Time; -0700 UTC it is observed during the summer the same way PST is observed during the winter in the US.