Why do Christians celebrate Christmas, when we don't know the actual date or time Jesus was born?

The answer is not to find the actual date of His birth, but to worship Christ and celebrate properly the entracne of the Son of God into humanity.  Christians should recognize the date that society has agreed upon when Christ was born, and use that "birthday" to spread the Gospel. 

Technically, Jesus was probably born close to December 25, although we don't know the actual date.  Jesus was baptized when He was 30 years old near the time of His birthday (Luke3:23).  According to the chronology of John 1:29 - 2:12,  He immediately ministered for approximately two weeks.  Then Jesus spent forty days being tempted (Mark 1:12-13).   Jesus then went on His first Galilean preaching tour (Mark 1:
14 - 45) for approximately two months.  Next, Jesus went to Jerusalem for the Passover Feast (John 2:13 - 25).   There are approximately three to four months between December 25 and Passover,  a strong suggestion that Jesus was born on or near December 25th.