In the bottom bar you have a tab for your open positions. On the price column you will see a โsellโ button.
After you click this, a dialog appears. When you sell with market order, you sell the share for the current price. Your order will be processed almost immediately.
Other option is a limit order, you can set your own price. When that price is reached, your order will be processed.
T212 is neither ahead nor behind UK time, you set the time for your account in the settings based on your location so that you get accurate times you can use to follow market activity.