When I first started Niaspan, I took it twice a day. I didn't realize that bedtime was the best time to take it. There is nothing wrong with taking it during the day, but I clearly had better results by taking it at night. I still had positive results when I took it during the daytime... just could have been better by taking it at bedtime.
I would suggest taking it at any time you want until you get use to it. Figure in a month or two, you should be better suited to Niaspan, and may want to then try it at bedtime.
Best of luck.