Dutch is my second language, my kids are Dutch, but they still sometimes struggle with the time.

"Tien voor half vijf" (ten before half five) is indeed 4:20.

"Tien over half vijf" (ten after half five) is 4:40.

Then when it's 4:45, it's "kwart voor vijf" (quarter before five).

I always have to think about it before I say it.