Welcome to the community!
@SLM2 wrote:... It is not my problem that you or the bank doesn't process payments on weekends. ...
Actually, it is. It's the customers' responsibility to ensure that payment has been received by the required date.
~taken from Terms of Service.
It's a similar situation with most credit cards and other institutions requiring payments by a certain date. You should note that it can take a couple of days for payments to be received, depending on method of payment (see here). In addition, as you are aware, you would also need to take weekends and holidays into consideration.
Hope this helps 😀