I am in the same boat, working while studying, and plan on doing the DL method for my ATPL exams for the conversion. From everything I have heard so far, if you study roughly 30 hrs per week, you can get it done in about 6 months. If you do about 15 a week, you can get it done in about a year. Obviously it varies from person to person and how fast they learn and catch on.
But the fastest I heard from guys getting it done was about 6 months, and a year being about normal.. so I guess those figures arent too far off.