I will always recommend ask your doc, BUT I have taken lithium for at least 5 years as part of my nightime meds. However, when I take nighttime meds is largely dependent when I get home from work and how frantic I am feeling for some relief by taking my meds. Many times I take them around 7:00pm with dinner and other times as late as midnight. It doesn't seem to effect my mood whatsoever as far as the lithium is concerned. I have noticed if I take it early I tend to wake up a bit earlier. If you have lithium levels drawn once in awhile, the blood has to be drawn before 12 hours after you nighttime dose, sof you take it at 7pm, your blood has to be drawn at about 7am. Something to keep in mind. On blood draw days I take the lithium about 10pm so I can go at a decent hour for blood draw.
Mighy help with your side effects if you take it with a meal. You have been on lithium long enough that I think you could "feel" any adverse effects by changing the time.
Bi-polarII; rapid cycler; Lithium 600
Requip XL 8mg; Lamictal 200 mg; seraquel 450mg, klonopin 4mg