Yes, CN most likely will be current in October. Yes, it's advisable to submit the DS-260 form, even for those processing AOS. The DS-260 form submission prior to OPT application has not impacted OPT approval AFAIK. DS-260 form submission in July is not too late. If you're planning on traveling back on F1 visa in August, you should hold off on the DS-260 form submission. Be aware even without the DS-260 form submission if you're subjected to secondary inspection for whatever reason, or they discover you're bringing in documents for the purpose of status adjustment, you might be denied admission. Entering the US on a NIV with the purpose of filing AOS is frowned upon, so you might want to think twice on that plan of traveling in August to get your documents. Go through the AOS spreadsheet for guidance on when to submit the AOS package.