I kept a very detailed view of each day I worked throughout the months it took me to get through the ATPL ground studies. It took me about 11 months.
The total hours I worked at home ended up at 650 or so. The brushup weeks and exam weeks were very long days. You'd finish at 5pm at the school and head back to the B&B for another good 6hrs of work. Each exam day saw a race back to the digs to continue cramming: I didn't record those hours.
I also had a full-time job too, so it can be done. Others just did the DL, but worked at it full-time. Some completed it all in 4 months.