Legal Holiday for Rent Due date?

I live in an apartment where rent is due on the first. the policy in our building is that rent paid after 5pm on the 3rd will be charged a 75 dollar late fee. All the tenants received written notice reminding us of the fact in October 2008. In the Month of Jan 2009 the 3rd fell on a Sat and the on site office hours on Sat are from 9:00am to 2:00pm. So I paid my rent on the 5th which is the first working day after the 3rd. The manager gave me a receipt that said I had a zero balance. In Feb 2009 I paid the rent on the 4th in full I also paid a separate money order for 75 dollars to cover the late fee for paying after the 3rd. This time when the manager gave me the receipt there was a different dollar amount for my account other than the monthly rent and late fee and this receipt was showing a balanced still owed on the account. I told the manager where was this balance from and she told me that it was a late fee charge from Jan that the management office told her to add to our account. This is on Feb 4. I then told her I needed to speak to the management office. I contacted the management office and also faxed then a written doent asking why when rent was being paid and our receipt would say one thing and then the following month it would say we owed a balance, that we did not give them the rent in full the previous because they take the late fee owed from the previous month first before applying our month to the monthly rent, and we have never received any written notification about any late rent we were being charged except once in 11/2008. I then stated on paper and over the telephone that I did not feel that i paid Jan rent late because sat and sun are considered business holidays and sent the civil code section which stated about being able to pay on the first business day following a sat or sun if the payment due day feel on the weekend. And although it was stated that we have until 5 pm on the 3rd because this 3rd feel on Sat was our time frame shortened to 2pm the close of the managers office? The management office then said that even if that was the case because the purchase date of the money order said the 5th I was still going to be charged the late fee. When I again referred to the legal codes she stated she did not care and that they have had to deal with this in litigation before and I was being charged it. I then told them that I was requesting a itemized list detailing the damages they incurred from me paying what they considered late to be able to come up with the amount of a 75 dollar charge. I also faxed a copy of this written request to them. She refused to give me her full name and then said they would have some one send it to me to date they have not done so. I paid my rent in full again minus the balance that they said was owed and now they are saying that I did not pay the rent in full plus have another late fee. I want to know being that I keep separate money orders that shows the amounts and what it is for If I am served with a 3 day notice that includes those amounts will it be voided for asking for an amount in excess of the rent? Also can they use the purchase date of the money order to say I did not have the funds by 5pm on the 3rd that fell on a sat when they office hours end at 2pm on a sat. Also I have a month to month lease so if they just try to give 30 day notice to move do I have enough grounds to say they are retaliating because I requested those details and told them I was contesting the late fee charge.