DST shenanigans aside (we're in the "US has changed but Europe hasn't" window), 10:00 in SF is 18:00 in London. Meaning their peak time window is 13:00–19:00 London time, or 14:00–20:00 Berlin time.

So us European folks get promotional rates during the morning and evening.

EDIT: Actually, because the promo ends at the end of March, it'll all be within DST shenanigans. So peak times are 12:00–18:00 London, 13:00–19:00 Berlin.

Outside 4pm to 10pm