It may be a trivial question, but I have a slip of paper in my passport saying to report on a Sunday.

I don't want to queue up on a Friday to be told come back on Monday, so if anyone knows what I should do then I would be grateful for your advice.

There is generally a grace period at all offices. Friday will be fine. Monday as well.

If the notification of staying longer than 90 days is made in person at the immigration office it can be made up to 10 days (or is it 14 days?) before the due date and up to 7 days after the due date without incurring a fine.

Several unhelpful posts removed.

The current window seems to be 15 days early to 7 days late for in person 90 day reporting.

Don't forget, most office allow 90 day notification by mail.

Thanks for your help.

Did my 90 day report in person 3 weeks in advance while I was getting visa extension with school and work permit at Amnat Charoen, last week. Not due until October 9th.

Some offices do allow making reports at same time as making annual extension of stay; but Bangkok and others do not and enforce the 15-7 day window.