The rotary breather valve functions to relieve pressure in the crankcase caused by the downstroke of the pistons and it controls the flow of oil in the lubrication system.
It is timed to engine rotation and opens after the downstroke of the pistons begins.
Opening and closing times are below but the exact opening-closing points vary between engines:

52-71 breather timing:
Opens at 77° after top dead center (ATDC) and closes 67° after bottom dead center (ABDC).
So the window is open for 170° of rotation.
Updates

• Install 72-76 pump.
• Changes breather timing - benefit.
• Modify feed supply.
• Plug old fitting in case.
• Run feed to back of new pump.

72-76 breather timing:
Opens 20°-25° after top dead center (ATDC) and closes 85°-90° after bottom dead center (ABDC).
And it's open for 245° (more duration than the 57-71 breather but closes later, less vacuum created).

This is the same as the XR model preferred specs. ¹⁾

A street oil pump has 2 slots and is driven at 1/2 engine speed. ²⁾
A racing oil pump has 4 slots and is driven at 1/4 engine speed.
All 4 stroke engines takes two revolutions before you come back to the timing marks being all aligned.

Left is the unmodified 1/4 speed R valve. Right is the 1000 stock.	R model is the left one.