First time I've chosen a seat in advance, forgive my ignorance!

When it says 'seat selection 7 days in advance', does that mean exactly 7 days before, at the exact time of my flight? E.g. if my flight was 7 Feb at 13.00, would I be able to select it tomorrow at 13.00 exactly?

Also, does it allow you to select any special seats? E.g. bulkhead, exit row, twin seats (at the back of the 747)? In CW, I assume it doesnt allow you to select upper deck seats?

Thanks in advance