Why is there an eastward increase and westward decrease in time?

The time is estimated at each place on the basis of position of sun known as local time.

There is eastward increase in time because Earth rotates from west to east and every 15 degree we go eastwards, local time is increased by 1 hour. There is westward decrease in time because every 15 degree we go westwards local time is decreased by 1 hour. The time is estimated to increase by 4 minutes towards the east and decrease by 4 minutes towards the west for every degree of longitude. Therefore, there is an eastward increase and westward decrease in time.