I have kept up the biphasic sleeping schedule for nearly 5 months, but I am still playing with things. I recently moved my nap times from the evenings to the mornings (from 9:00pm to 9:00am). This was mainly because the evening naps were really shortening my evening time, and thus my "down" time and I think this was starting to burn me out. After working out, fixing and eating dinner, and running personal errands, I wasn't able to sit and rest until 8:00 or 8:30, giving me at most only an hour before nap time. The rest of my awake time was spent working on personal projects, or client projects. Apparently, I need more time to do nothing!
With the new schedule, I now have more options for relaxing. The nap does cut into my workday a little, so I have been trying to make up "billable" time in the evenings. Currently I am doing a 4.5 hour block of sleep beginning at 1:30 am, sleeping until 6:00 am or so, doing a few hours of work, and then taking a nap from 9:00 am until 10:30 am. I think this may work well, since I generally wake up at 10:00 or 10:30 if I'm just naturally left to sleep. This might be more in tune with what my body wants to naturally do. While it does break up my workday, that isn't necessarily a bad thing, since I generally have at most a 2 hour attention span for working on any given project!
So far it's all working really well...we'll see what happens if I try to shift back down to 4.5 hours of total sleep. The main awake period may be a bit too long for 4.5 hours of total sleep...but who knows, I may give it a shot in the coming weeks.