Unfortunately, most applications estimate how long your render will take based on how long recent frames have taken to render, multiplied by the number of existing frames left to render. It's not uncommon for applications to 'guestimate' incorrectly if the amount of render time (per frame) changes over the course of the composition that needs to be rendered. Your "more than a day" may vary. (and get worse/longer?)
Anecdotal evidence (from may applications that give render estimations):
Some renders that estimate a long time change to short if the computational requirements go down.
Some renders that estimate a short time change to a long total render time if the comp becomes more difficult to render at the end.
Hardware will always change the result of estimations.
Render a sequence of frames from After Effects.
Once they are complete, compile them into an mp4.
- You'll potentially save some headache
I agree with KoMaruyama that you should render to an image sequence first - especially if a render is going to take a long time.
What is in your project? I mean, you have a pretty weak computer, but a day for 12 seconds seems to indicate some pretty complex stuff. Did you accidentally turn on the ray-traced renderer?