Constant MAX_TTL 

pub const MAX_TTL: u32 = 86400_u32 /* 86_400u32 */;

Available on crate features dns and hickory and std only.

Maximum TTL. This is set to one day (in seconds).

RFC 2181, section 8 says that the maximum TTL value is 2147483647, but implementations may place an upper bound on received TTLs.