Is there any way to measure this with an Oscilloscope?
measure the led on/off time with the Oscilloscope if the osc is correct then the on/off times will be as per your code


I would leave CONFIG PWRTEN = ON


AND ADD THIS
OSCCON = %01110000 ; 64Mhz
OSCTUNE.6 = 1 ; Enable 4x PLL
while ! osccon2.7 :WEND

to make sure the pll has stabilised before you run any other code , if timing is critical