1. January 1, 2007 for all newly constructed single family and multifamily dwelling units for which building permits were issued on or after January 1, 2007.
2. August 1, 2008 for all existing single family dwelling units.
3. August 1, 2009 for all multifamily dwelling units

1. Register on the site for an account.  This allows you to keep track of the ads you are running. 
2. Make sure you always upload digital pictures of your apartment.  Many tenants say they will not even call on a listing unless they see pictures. 
3. Always include your phone number, but never include your email address.  Instead, use the built-in anonymous feature to avoid getting spam, as the spam senders comb these sites looking for email addresses to add to their lists.
4. Put as much detail in the ad as possible, including the rent, exact street address, pet preferences, application fee, damage deposit, etc.
5. With 25-50 posts per hour, you should re-post your ad every couple of days.  Many people never scroll past the first page when looking.
6. Use the "My Account" section to re-use generic ads to speed up posting.  Also use this section to remove your previous ads and then simply click a button to re-post them.

I have also had great luck with "reverse prospecting" on Craig's List.  I click on the section for "Need Housing" and search through there every couple of days looking for people that need apartments near my properties with vacancies.