What is mean of fast/slow 0C/85C model?

You have already been answered but I can visualise the timing space as a triangle with 3 corners, top corner being best for timing:

corner 1 is the 0C fast model. Best for timing

corner 2 is 0c slow model

corner 3 is 85C slow model

All cases fall on the triangle space.

Definitions are given by altera as follows:

0C fast: fastest silicon + highest voltage + 0C

0C slow: slowest silicon + lowest voltage + 0C

85C slow: slowest silicon + lowest voltage + 85C

Note: voltage within allowable range, silicon within chosen speed grade

since corner 1 is best, I note that timequest gives fmax for corner 2 & 3 but not corner 1

To be more accurate, it is not a single triangle but imagine three axes say x,y,z where x is for temperature, y for voltage, z for silicon. at every case you can choose 3 points, one on each axis and draw a triangle. The centre of a given triangle becomes the timing space of your case. The whole set of triangles is the full timing space.