Hello @klaudia_dudczak ,
Generally speaking, you should not render to .avi. If it crashes at any point, you lose everything. Standard practice is to render out a sequence of frames (exr or png usually for me) and then use those frames to create a movie file.
That being said, you might be able to click and drag the bottom of that window to see if it expands, maybe it's just cut off.
Otherwise, the most likely reason why it can't predict the render time is because typically it averages out the time per frame to give an estimate, but since you are rendering to a single file it doesn't know how to do that because it doesn't have any information about previous frames. I'm guessing about that, but if you switch to frames you'll get a decent idea of the overall time after it has rendered 4-6 frames usually.
Best Regards,