H1B Validity period from I797B

In my petition approval document(I797B), Validity is mentioned between two dates. What does it signify ?, Does it mean that visa is valid from between these two dates or the visa validity period will be decided by the VO during the interview ?

The dates mentioned in the I-797 determine the duration within which your H1B petition is valid. One can go for VISA stamping with the I-797 only during this petition validity period. However, your H1B VISA validity is determined by the VO at the consulate.