Nameservers with same IP, can cause high time to first byte?

[postcd]

Hello, when analysed domain by intodns.com i got:

Different subnets - WARNING: Not all of your nameservers are in different subnets
Different autonomous systems - WARNING: Single point of failure

Its because my nameservers are both pointed to same IP. How can this influence time to first byte? Meaning wait time when website load / resolve time. Can this be even 500 miliseconds slower? thx

 

[Pantek Support]

This shouldn't influence "time to first byte" necessarily, but having both nameservers pointed to the same IP address is not recommended because as the WARNING suggested, it does present a single point of failure. If you have an outage or issue on that IP address or subnet, all your DNS lookups globally will fail.