It's never 100% for me but I know what you mean. Occasionally I'll hit tree throughout the day and it's just like I'm going through the motions. Come night-time, though, my sessions seems much more relaxing and-- err..... "fulfilling?" I get more of what I want to get out of my weed high at night sometimes, is what I'm trying to say.
I always felt like it was because at the end of the day, most of the BS stress is gone and my mind's finally starting to slow down and de-clutter. When I smoke all worked up and anxious through the day, the anxiety goes away a bit but it's still there. Come night-time and it's almost like I'm starting with a clean slate, so to speak.
(Sorry if I'm not making sense, I feel kind of.... weird today. Like my thoughts are all over the place and jumbled and stuff, finding it difficult to choose words that are accurately conveying my thoughts this morning.... Weird....)