1. Leviticus 7:16 (ESV)
  2. Exposition

How was the the vow or freewill offering treated differently than the thanksgiving offering?

Leviticus 7:16 (ESV)

16 But if the sacrifice of his offering is a vow offering or a freewill offering, it shall be eaten on the day that he offers his sacrifice, and on the next day what remains of it shall be eaten.

The stipulations regarding the vow and freewill offering are less strict than those of the thanksgiving offering. If the entire offering could not to be eaten right away, it could be consumed on the following day.