20.45 in CET is 19.45 in GMT. This is because CET which is Central European Time is one hour ahead GMT which stands for Greenwich Meridian Time. This is otherwise known as GMT +0100. Albania, Andorra, Austria, Belgium, Bosnia-Herzegovina, Croatia, Czech Republic, Denmark (mainland), France, Germany, Gibraltar, Hungary, Italy, Kosovo, Liechtenstein, Luxembourg, Macedonia, Malta, Monaco, Montenegro, Netherlands, Norway, Poland, San Marino, Serbia, Slovakia, Slovenia, Spain - except Canary Islands, Sweden, Switzerland and Vatican City. These countries make up a large proportion of mainland Europe.
CET is only a time zone in these countries for 5 months of the year. Just like Greenwich Meridian Time in the United Kingdom changes to BST - British Summer Time, CET also changes. This change occurs on the last Sunday of March each year and the new time zone is CEST - Central European Summer Time. This change was originally so that there is more light in the afternoons and therefore good for economies with more sunlight in the evenings after the working day is over. Sports and retail have seen huge benefits from Daylight Saving Time and some countries have shown a decrease in energy consumption during summer months. This method of daylight savings time was once observed all over the world with most countries changing the clocks forward in the summer months.
Asia, South America and some parts of Australia and Africa no longer observe this change in time due the 24 hour society that we now live in which allows retail and sporting events to be held when it is dark outside. Asia and South America also have a larger amount of agricultural workers, who this method is criticized by for changing the working farming day.