Big businesses could abuse such a deadline by not respecting the requests to opt out, by not providing an email address or a link to their web site to make a request to opt out. They could abuse the situation until the 29th day.
That is why we thought 10 business days was reasonable. In the case of a minor sports team, it simply has to make sure the next time it sends out solicitation emails that it checks its list again to avoid sending unwanted emails.