I never do a cover verbatim. I always give the song a new arrangement. Otherwise, what would be the point? It's already been done. It's different if you're in a cover band that plays clubs. In that situation, you'll get more work by trying to perform a song as much like the record as possible. But I see no point in recording that myself.
I often make solo acoustic fingerpicking arrangements of old songs, and it takes a long time to come up with an arrangement that's worthwhile. I realize that's a whole different thing. I'm just throwing it out there. I might spend a month or more on composing a solo guitar instrumental whether it's original or a cover. I was faster at it when I was younger. You'll find it harder to get motivated in your creativity when you get older. (I'm 59.)
As far as writing original vocal tunes, I could knock one out every week or two. I'm fairly prolific with the music; it's the lyrics that take time because I want every word to be exactly the right word, but the backing music for a vocal tune is fairly simplistic compared to a solo fingerpicked tune.
I also tend to work on several new pieces at once. It's like reading books. I'm one of those people who has several books on his nightstand and read them all a little here and there as the mood strikes me.
Oh well, that probably wasn't much help, was it?
Good luck,
Bill