Guild Wars 2

I understand that the one-time-event tomorrow will take place at 19:00 PM, which is normally 7:00 PM for the UK, but, the clocks are being pushed back one hour here thus making it 6:00 PM, will it still be 7:00 PM in-game?

The event will be at 19:00 pm in the UK tomorrow, we are currently in BST and when the clocks change we will be going to GMT.

19:00 GMT takes the time change into consideration. 12:00 PDT was 20:00 BST in the UK today. Usually there is an 8 hour difference between Pacific Time and UK time, however there is a small period where it drops to 7 hours until the USA change the clocks too.