Very short. "Got a good thing goin'" came out 10/66, only 8 months before "Let 'em roll". Maybe it didn't sell well.
Soul stream would be better able to answer that, but I think the difference between "Let 'em roll" and "Certain feeling" is quite huge and indicates a lot of work on John Patton's part. There was a complete break with his former colleagues (partly because GG was out of it) and a radically different approach.
Looking through the BN discography, there doesn't seem to be any notable hiatus between the two recording dates, except for about 5 weeks in late summer of 1967, when Alfred Lion actually retired. So I think it was down to John, feeling ready to record.
MG