It really doesn't matter when and how you visualize. I personally find it better to do it when I'm taking a walk or taking a relaxing drive or if I'm bored. You shouldn't force yourself to visualize either, forcing it just sends vibes that you need it, then you keep needing it. The reason people say to do it before you go to bed is because you're in a relaxed state and energy is transmitted more easily and it might reprogram the subconscious more easily. I've never been able to visualize very well at night, so if you find it easier to do it when you're out and about during the day, it will be more effective for you anyway. Everything is supposed to feel easy right? So just do whatever feels best and easiest for you, and you will manifest what you want. All you really need is belief and trust something will manifest anyway, visualizing isn't even necessary. So if you don't feel like visualizing? Don't even do it. Visualization is just a tool to make you feel good, if you have to make yourself do it then it's not going to be effective.

The most important thing is your feeling while you are visualising. Even if you can't really see clearly, you know who or what you are seing, right? Just concentrate on the feelings.