I transfer to secondary when the SG is 1.010-1.030ish. That way, fermentation continues but the wine is safely in the carboy and airlocked.
Thereafter, I rack every 45-60 days whenever there are lees 1/4" thick or so.
Winemaking is a great hobby for busy procrastinators, and it can stay in secondary for years as long as it's not kept on the lees. I just bottled some rhubarb wine last week. It was made in early 2008, and had been in the carboy for at least 15-16 months!
Broken Leg Brewery
Giving beer a leg to stand on since 2006