Mine is very finicky. Some nights we're in perfect harmony, night turns to day and vice-versa without either of us realizing. Others, we can't find a single thing we agree on and the day and night escapes us. Had to have a long conversation about getting some sleep with them.
I found we work best sometime between 8pm - 11pm to start, with our time going for as long as we're able to stay awake, sometime the entire night, others for maybe an hour.
More often than not, it's midday between 10am and 4pm where ideas seem to flow naturally, with 1pm being our natural peek.