Joe and Guilliaume are correct (as always): It takes a lot of exposure, and it will look overexposed when it's right. I use Tetenal gold toner, which doesn't seem to bleach as much as some other toners. Also I feel that the "bleaching" in the fix is not so much a bleaching as a colour change, where the lighter (browner) tone during fixing looks like a bleaching action.
When that is said, I use extremely dilute rapid fixer to bleach the highlights back if they seem veiled - 1:40 or so instead of the 1:4 you would use for "normal" prints.
POP is a great process, capable of stunning results with a tonal scale which just cannot be compared to any modern paper or process. Ideally the negative should have extreme contrast, but the contrast in the print can be adjusted by exposing in direct sun and/or partial shade. "Northlight" gives higher print contrast from a given negative, which is useful for any kind of normal negative. Of course that means that the exposure time will be hours or days instead of minutes, so it's a good idea to start with very contrasty negatives in direct sunligh.