When bride and groom came from different parishes the banns were read in both places. That accounts for there being two records. The date is likely to be the date the couple "contracted", i.e. told the session clerk they intended to marry, hence the different days. Until you read the original entries, you won't be absolutely certain. You should read both as the detail can vary. They can both be seen on ScotlandPeople:
Jeremiah Olipher & Mary Newtown 21-10-1738 parish of Hownam
Jeremiah Oliver & Mary Newtoun 22-10-1738 parish of Southdean and Abbotrule