For every yowl or widdle protest there is always confusion about timezones. Often the times are stated in UK time.
Generally they happen at 9pm UK time, which in winter is 9pm GMT. There is an example yowl timezone equivalents set for a 9pm GMT yowl here.
Summer is one hour ahead of UTC/GMT, and known as British Summer Time (BST).
I have put in an example yowl time here, which gives other timezone equivalents for a 9pm (BST) yowl.