The "DEF CON CTF" Qualifiers end May 29, 2023 00:00 UTC

[number6]

Announced on https://defcon.org/
https://nautilus.institute/ has:
Qualifications begin: May 27, 2023 00:00 UTC (or 32 bit clock with number of seconds since epoch of Jan 1, 1970 GMT-0: 1685145600) for DEF CON 31 CTF
Qualifications end: May 29, 2023 00:00 UTC (or 32 bit clock with number of seconds since epoch of Jan 1, 1970 GMT-0: 1685318400) for DEF CON 31 CTF

Sign-up appears to be:
https://quals.2023.nautilus.institute/