ESP8266: sntp_startup_delay_MS_rfc_not_less_than_60000

in the ESP8266 Example NTP-TZ-DST.ino you find following comment

// OPTIONAL: change SNTP startup delay
// a weak function is already defined and returns 0 (RFC violation)
// it can be redefined:
//uint32_t sntp_startup_delay_MS_rfc_not_less_than_60000 ()
//{
//    //info_sntp_startup_delay_MS_rfc_not_less_than_60000_has_been_called = true;
//    return 60000; // 60s (or lwIP's original default: (random() % 5000))
//}

Can anyone point me to that RFC where this 60 seconds are defined as mandatory?
I find the 15 seconds of the polling intervall in the "best practices" of RFC4330
https://tools.ietf.org/html/rfc4330#page-21

but no limitations on the start delay.

When the client is first coming up or after reset, randomize the
timeout from one to five minutes. This is to minimize shock when
3000 PCs are rebooted at the same time power is restored after a
blackout.

leasons learned:

read more than one page of a spec ^^

Thank you Juraj.
karma+

I first thought, why this setting? then I realized it is for the boot of many devices at once. So I searched for "boot" in the RFC.

again me:

the RFC4330 is marked as obsolete and replaced by the RFC5905 (as I understand, RFC4330 was incooperated into chapter 14 of RFC5905) where in RFC5905 is the evidence that this boot delay is required in a SNTP implementation?

... I'm still searching an evidence for the need of the 60 second delay for the first SNTP call based on the RFC5905 (?). Any new hints?