Hi Geoff,
To be honest I'm not certain but these would be very close
50 for 20 minutes
http://www.howtobrew.com/section3/chapter14-4.html
"Malted barley also contains a lot of amino acid chains which form the simple proteins needed by the germinating plant. In the wort, these proteins are instead utilized by the yeast for their growth and development. Most wort proteins, including some enzymes like the amylases, are not soluble until the mash reaches temperatures associated with the protein rest (113-131F). The two main proteolytic enzymes responsible are peptidase and protease. Peptidase works to provide the wort with amino acid nutrients that will be used by the yeast. Protease works to break up the larger proteins which enhances the head retention of beer and reduces haze. In fully modified malts, these enzymes have done their work during the malting process.
The temperature and pH ranges for these two proteolytic enzymes overlap. The optimum pH range is 4.2 - 5.3 and both enzymes are active enough between 113 - 131F that talking about an optimum range for each is not relevant. This optimum pH range is a bit low with respect to most mashes, but the typical mash pH of 5.3 is not out of the ballpark. There is no need to attempt to lower the mash pH to facilitate the use of these enzymes. The typical Protein Rest at 120 - 130F is used to break up proteins which might otherwise cause chill haze and can improve the head retention. This rest should only be used when using moderately-modified malts, or when using fully modified malts with a large proportion (>25%) of unmalted grain, e.g. flaked barley, wheat, rye, or oatmeal. Using this rest in a mash consisting mainly of fully modified malts would break up the proteins responsible for body and head retention and result in a thin, watery beer. The standard time for a protein rest is 20 - 30 minutes."
For the Farenheit challenged 113 - 131F is 45 - 55c
63 for 30 minutes
68 for 30 minutes
I use direct heat on the tun and allow about 5 - 10 minutes between rests to get to the next temperature.
Don't extend the 50 much past 20, the others can easily be increased to 40 minutes each if you want.
Hope that is helpful
Steve