Hard to say, but 1 song a day or so would be a fair guess. It depends on a lot of things, but I doubt it would take more than two working weeks maximum. One would be possible.
Mixing is a lot more difficult than you might think. It could easily take a month or more to mix. There are complications too numerous to mention here, but one as an example.....
When you introduce another instrument to a mix it will often change the sound of the other instruments. So in those particular areas you need to change not only volume of various instruments, especially if you're trying to change the emphasis on the mix, but the EQ for the other instruments may need to be changed at that point to cut through the mix. Then when the instrument is removed, the EQ, etc has to be changed back, all while preventing the listener from perceiving the difference.
Now on top of that is ear fatigue. After you listen to the mix for a while, you start to lose the ability to sense accurately the sonic quality of the mix. You actually need to get away from hearing it to be able to critique it properly. It sounds great today, crappy tomorrow. Now just throw that one example into a DT song, and you can easily see where it could take a long time. I've done a lot of mixing myself, and helped my son in law who used to have a recording studio and does his own mixing, etc. for his own albums. He has routinely spent over 1 week just doing 1 song.
Then on top of that, the producer (JP) comes in and says he doesn't like something, now throw that mix out the window and start over.