Please find the information regarding this case below.
I had a discussion with one of the senior engineers. Following is their reply.
If the TTL set by the nameserver is in between the Minimum and the Maximum DNS TTL value, then the NetScaler will only forward the TTL value provided by the name server.
However, if the TTL value set by the nameserver is in between lower than the Minimum value or higher than the Maximum value then NetScaler will set the min. or max TTL value configured on it, depending upon the situation .
Hope that answers your question. Please let me know in case of any queries regarding this.