You are on the right track, but you are wrong.
Credit cards have 3 important dates. First, the statement date. Second, the reporting date. Third, the due date. Sometimes the statement date and the reporting date are the same, but most of my cards have reporting dates that are different from the statement date. You want all your cards to have the balance you want reported on the reporting date.
I try to keep all my cards under 10% on the reporting date. If I wanted to further optimize my score, I would have one card report between 1-9% and all the others report zero balances on the reporting dates. I gain around 5 points by doing this (not really worth it). As long as all balances are under 10% you should be fine.
Reporting dates can be tricky to determine since most credit reports don't mention them. Credit Karma allows you to see the date your CC last reported if you are still using the TU only version. For those who also have access to Equifax reports, apparently the UI has changed and you don't get to see it anymore.
Finally, reporting dates sometimes are off by a day or two. For example, my CU Visa usually reports on the 14th, but last month it reported on the 15th. For me keeping under 10% balances are easy since most of my credit limits are over 20k. If you have high spend or low limits you might need to worry about reporting dates, but for usual credit purposes it probably does not matter unless you have low scores or borderline scores.
