Short Answer: Reduce the exposure time.

Long Answer:

The process you're dealing with one where that light from your subject strikes the paper and causes a reaction in the emulsion on the paper, then the developer reacts with the emulsion in the paper to turn it black. How long that process takes is a function of three things:

• Exposure. More light makes the paper turn black more easily. Papers vary in speed, but yours appears to be a generic variable-contrast RC like the Kodak and Ilford papers commonly used for printing.

• How much developer it's exposed to. This is governed by dilution: less dilution means more developer is available to react with the emulsion and more dilution has the opposite effect. The dilutions in the Tetenal data sheet would apply to the papers described above. I'd stick with the 1:9 ratio since you'll get more out of it and slower times give you finer control over when you pull the paper out and stop it.

• Temperature. In most chemical processes, warmer temperatures increase the reaction rate. I'm going to assume you have a good handle on the temperature of the developer when you start using it, because even at 30°C, Tetenal should still take about 30 seconds to develop a sheet of paper when diluted 9:1.

Normally when you're doing printing at an enlarger, you'd put a strip of paper on the easel, make a graduated exposure, develop it, pick the graduation that gave the best results and then make the print on a full sheet. Since you don't have that option with your pinhole prints, you'll need to adjust exposure time (the one variable you can control) to find what works with the nominal developer temperature and dilution.

The time your paper is taking to react says it's seeing far too much light. I'd start by cutting the exposure down from 60 seconds to as little as 15 or 20.