It's my understanding that you can do your 90 day reporting within 7 days of your listed reporting date.

1. Does this mean 7 days before and 7 days after?

2. If I can report within 7 days after will I incur a fine, for example, I report 5 days after my listed reporting date?

You can report in person 15 days before and upto 7 days after the report date.

By mail 15 days before only.

As said it you can report up to 15 days early or 7 days from the report date (including the report date).

If you are later than 7 days from the report date you can be fined 2000 baht or up to a maximum fo 5000 baht.

If reporting by mail to Bangkok immigration you must mail your report no later than 15 day early. For other offices you need to check for their rules because the may different. Some only require the report to arrive by the report date, There are also some offices that do not allow 90 day reports by mail.