Do you happen to be studying through the Open University? I had a very similar experience studying maths part time. My first couple of years were basically just doing the assignments a few days before they were due, and then cramming for the exam.

I did eventually manage to get into the habit of doing more consistent gradual work throughout the year, and that's the only advice I could give. The habit of devoting that hour or two per day became the norm and I no longer had to struggle to force myself to study (or fail to).