Is this late fee legal in Texas?

Hi, I have a question about Texas rent laws. I am a community manager here in California and I am very knowledgeable about our laws here, but not familiar with Texas law. My cousin is currently renting an apartment that has removed the rent drop box from the office due to theft. She now has to rely on office hours and whether someone is in the office to pay her rent. Over this holiday weekend, she went to pay rent on 9/5 with a money order dated 9/4 but the office was already closed. It is usually open 8-5 on Saturdays. They were closed Sunday and Monday so she went in there today to pay. The manager refused her rent because it did not include a late fee. Is this proper or legal to refuse rent if it does not include a late fee?

In this case the PM should have taken the payment that included the initial late fee being it was dated and the office was closed. I do know of several properties that have removed their drop boxes due to potential theft. My personal thought is if they remove the drop box they should have an alternative way to pay ie: online (at least through the end of their grace period). Just one PM's opinion.

Is rent due on the 5th? Or is it due on the 1st, but with a grace period through the 5th? It makes a difference. Also, were residents notified of the office closure on Saturday for the holiday?

IF rent is due on the 1st, and residents were notified, then I would agree with the late fee. Especially since I would imagine that the removal of the drop box included some sort of statement that rent would need to be paid during office hours. At least, I would hope so.

In most places, rent is due on the 1st. I explain to my residents that even if there is a grace period with no late fees through the 5th, rent is still late on the 2nd...there just aren't additional fees at that point.