The gospel song with the lyrics "it's harvest time" is called 'Harvest'. It was written and recorded by John P. Kee, and I've included a link to the lyrics below, so you can double-check that this is in fact the song you were looking for:
John P Kee is an American pastor and gospel singer. His love of music developed at an early age and he became a member of several singing groups.
When he moved with his family from North Carolina to California at age 14 he had a hard time adjusting so he left and moved to Charlotte, North Carolina. However the part of the city he lived in was known for drug activities and violence.
One of his friends became involved in a drugs deal that turned bad and the friend was murdered in front of him. He attended a revival meeting and during a visitation, decided to dedicate his life to God.
Kee became an ordained minister in his mid twenties and went on to become the founder of the New Life Fellowship Center where to this day he is the senior pastor.
The church is located in the same area where he once led a life of crime and drugs.