The deadline for IAC Rules Change proposals is July 1, as noted in Section 1 of the IAC Contest Rules. If you're planning to propose rules changes, the best way to do so is to go to this address:
https://www.iac.org/propose-rule-change, fill out the form, and hit "Submit". IAC member login is required.
If you happen to be an IAC member but for whatever reason can't use the above link, you can send a proposed change to ruleschair [at] iac.org…