It usually happens when you least expect it, when you truly let go. You cannot know when it will happen, or what it will be like. You especially cannot MAKE it happen, so just keep practicing
As for the day/night thing. This is not a meditation thing, this is a sleep/wake cycle thing. When you wake up in the morning you usually have a burst of planning thoughts etc, it takes some time for this to calm down. Later in the day you are usually much more settled. It's ok to have racing thoughts in equanimity, happened to me all the time, just note and notice, it's not indicative of a bad sit.