Apex domains cannot have CNAME records.
Question and response
Question
dig 223.52.92.in-addr.arpa. NS
Answer
223.52.92.in-addr.arpa. 5 NS ns4.zerotimeservices.com.
223.52.92.in-addr.arpa. 5 NS ns5.zerotimeservices.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0