possible cause for this behavior?

I physically pay most of the family's bills but I ask my husband for (and usually receive) payment from him for his share of joint bills (mostly our daughters' expenses).  Right now, we're living separately, at my request.  

As usual, I had told my husband several weeks in advance how much he would owe me for joint bills for September.  I reminded him a few times.  He assured me he would pay in a timely fashion.

The date by which I asked him to pay has come and gone.  It turns out that making a transfer from his dad's bank account (he is a caregiver for his parents) to his account will be more complicated than he thought.  

So, people with ADHD and those without, what do you think:  did my husband wait until the last minute (and perhaps beyond) because he thought the task (paying me) would be easy or because he thought it would be hard?