"Frühzündung" means ignition advance. This is also what Dappsull meant when he wrote "early ignition timing".
I'm absolutely not familiar with R2 particularly, but if the manual points out the maximum advance angle, or piston position in mm before TDC, ( 9 mm ?)
then you should set up your ignition-lever and assembly, that it is not possible by no means, to advance timing any more than that.
This will avoid engine damage, e.g. if you are distracted and adjust the lever to far / timing to much advanced.
First of all, you should get or make yourselves a timing-disc. This can be printed out and glued to an old CD for example.
Fix this CD on your crankshaft front end (if possible on an R2). Also fix a stiff wire somewhere in that area and bend, to have a fixed pointer/indicator.
Now you need a fixed piston-stop. I'd take an old sparkplug, remove the ceramic isolator with a chisel or so, then punch an appropriate wooden dowel through.
Wide enough, that it protrudes inside the head. Not important, how far, but far enogh to stop the piston.
Now turn the crank carefully in one direction until the piston stops. Make a mark at your wire-indicator.
Now turn the crank the opposite direction, until it stops again. Set the second mark on your disc.
Now make a third mark on your disk exactly in the middle between the two other marks, in that sector, where you can't turn the crank due to piston stopper.
This is your exact TDC ! Now you can mark your flywheel through the inspection hole with a centerpunch. So you can find your TDC much easier in the future.
You could to the same for the maximum advance. Not with a piston stop, but by measuring the distance from TDC like given in the manual.
This will make things easier and avoids missreadings and mixing up things for the future.
Hope this helps.
I had a look into your link and it says for "Frühzündung" (ignition advance) "rd9,5mm", which I would translate to "roundabout 9,5 mm" = circa.
The manual also recommends, (Page 17 far below and page 18 top) :
"Ignition lever has always to be set appropriate for engine revs. On low revs give only half advance-range.
Full advance only for high revs and low load, e.g. on level roads, or in low gears.
A clanking or clacking noise from the cylinder is often the consequence of too much advance."
(this is translated with my own words)