Translation:It takes four days.
It means "interval of time," because the sun takes a while to rise behind the gates. There are two parts ("radicals") to this kanji (the gates and the sun), and they both get smacked together into one single kanji to make the word.
Every kanji has a story, and once you learn it, it is easy (and fun!) to piece the radicals together to get the meaning. For example, if you have this word: 聞く, then the story behind it is that you have an ear (耳 - pronounced みみ if it's by itself) listening at the gates (門 - pronounced もん by itself). But the new kanji, since it is basically a picture of an ear listening at the gates, gives you "to listen" or "to hear" (きく, or if you put that into its polite version, ききます).
Fun stuff! I make my students look at "Read Japanese Today" by Len Walsh. It was originally written for business travelers in the 1960s but there is an updated version which I haven't seen (since the old one does my students just fine). There are a lot of other books that make up stories about the kanji, but frankly, I don't see the point when the actual evolution of the kanji is more interesting, and you get a window into the cultures of ancient Japan and China.
Hope this helps!
The kanji for numbers and day/sun have multiple readings and changes on what it is being paired up with (or if it is alone). The word for month/moon also changes depending on if it is alone or what other kanji it is paired up with. Idk exactly why it changes, but it is something we just have to learn. (-: