In case you haven't seen it, here is a good article on Waldstauden rye (which is very likely the variety that
Sepp Holzer is growing):
http://www.fondazioneslowfood.com/en/ark-of-taste-slow-food/waldstauden-rye/
In terms of planting, the article says:
It places minimal demands on the soil and is sowed around Johannis Day (24 June). The young cereal plants are subsequently grazed (or also mowed) which promotes stocking. After stocking, the plants develop over winter and then form heads relatively early in spring.
So basically, it is a winter rye... but sown in spring. The mowing prevents it from flowering so that it doesn't die off the first year -- and then it is allowed to reach maturity in the second year and produce. Much of the reason ryes were cultivated like this (Waldstauden, and a similar Norwegian variety called Svedjerug Tvensberg) was for purposes of weed control, stacking of functions in terms of providing animal fodder, and to synchronize nicely with the correct seasons for burning. From what I can tell, they aren't fundamentally different than a simple winter rye.
If you plant it now (fall 2016), you could probably get a yield in spring 2017, but not as good of a yield as if you plant in spring 2017 and harvest in spring 2018. But you will probably get a heavier total yield if you can harvest in spring 2017, turn around and immediately plant a larger area. Basically, you can probably get another growing season.
As always with rare seed, though, it would be wise to reserve some in storage in case some disaster occurs to the crop.
Speaking of rare seed, holy moly good job finding those seeds!!! I've been trying and failing to track some of that down. Is there any possible way you can share some? I'd be glad to purchase some, or trade you any of the perennial grain varieties I've managed to track down so far. You can see a list of my seeds and projects at
http://jasonpadvorac.com/perennial-grains/