I'm pretty sure this is the opposite of what he should be doing :/
I had a great betta who recently passed -And always slept at night. He was also very feisty and always flaring at my fingers, which I loved - the new guy is very passive and only comes out of his cave in the evening. ..Does this happen sometimes or could he be sick? Maybe the lights in the petstore got him off schedule?
How long have you had him? Often times they adjust to your time-frame. My boy is a late riser and a night owl like I am. It is funny to turn his light on too early, he's quite pathetic waking up too early