If the bill was due on the 28th, and you paid on the first, then whether posted on the first or second, you'd still be late.
Which CC is it and did you have a late added on your CRs? If not on your CR, then I would worry about it.
Each CC has their own rules. I keep a list with me on what the rules are with each CC. HSBC, for example, requires payment by 4pm on the day prior to when it was due. My National City requires payment by 5pm on the due date, but you can't pay and be credited on Saturdays. YMMV.
If a late was added, you could fire off GWs to get them to change it.
A moderator here, masdeocho, made a great suggestion once. Pay the minimum immediately upon receipt of the statement or notification of a statement (if online). Then, that would give you flexibility to pay later at a higher amount, if so desired, and prevents you from forgetting that a payment was due.