I don't think that sounds completely natural translated directly to Swedish, but it would be somewhere around the lines of "Jag tycker om när mina morgnar är långsamma" (literally: "I like when my mornings are slow").
The difference is that in Duolingo's sentence, it's the slow mornings as a whole you like. The noun and the adjective come as a bundle so to speak. In your sentence, you like your mornings a certain way. The adjective is "added" to the noun.
I would agree with this. And it corresponds perfectly to grasse matinée ... get up late, do some small things (or nothing) ... have a long cup of coffee with the newspaper (The Sun...) ;-)
And by mid afternoon "start thinking" about what you could do ... (your wife may have asked you already a few times by then ...)