This may not be what you're looking for, but this page contains a "Christian poem" called "Hell Is Real" which contains the phrase "I thought I had plenty of time." The same poem exists at several other web sites.

Here is an advertisement for Best Of The American Country Hymn Book. Its contents include a song called "Plenty of Time" written by Clay McLean and Henry Slaughter, copyright 1970. I was unable to find any other information about this song.