1200 RPM is not idle, and will allow full oil pressure...
First start of an engine is pretty hectic; verifying oil pressure, listen for knocks, setting initial timing to get it to run smooth and not choppy, verifying no oil, trans fluid, or coolant, or fuel leaks, that's an easy 3 - 5 minutes right there... Then get it up to 2500 and set total timing, then watch the temp gauge to make sure it doesn't overheat...
If there are any issues that are critical and make you shut it down to fix so it doesn't blow up, it doesn't matter if you were at 1200 or 2500 RPM before you shut it down... Verify there are no issues before starting the break in...