How accurate do VGA timing signals have to be?

I'm looking to try to drive a VGA monitor using a PIC 16F690, on a 12MHz clock (3,000,000 operations per second)

The most accurate the signal from the PIC can be is 1/3 uS, but the timings given are to 1/100 uS for the 640 X 480 @ 60Hz standard.

Overall, each frame does come out to a whole number of cycles, so does the exact duration of each line matter?

I've seen a PIC output very basic graphics on a 4MHz clock, so I would expect it to be fairly simple to just light up the display on 12MHz.

Alternatively, is the display smart enough to fit whatever is fed into it onto the screen?

Thanks for the help.