Answer:
Except for Re-presented Check Entries (RCKs), any ACH debit entry that has been returned for insufficient funds can be reinitiated within 180 days after the Settlement Date for the original Entry. However, an Originator or ODFI must not reinitiate an Entry that has been returned for insufficient or uncollected funds more than two times following the return of the original Entry.
In plain English, you get three shots at it, counting the original entry.
Reference: NACHA Rules, subsection 2.12.4 - Reinitiation of Returned Entries.