Child passport renewal online (UK)

hi all Am having issues taking a photo of my son (9yo) that is graded GOOD by the passport service checker. The best photo I have is FAIR. I would like to ask the forum if they have any negative experiences on submitting an online application with a FAIR graded photo (either delay or rejection) Also is four weeks enough time to allow for a child renewal online? The current graph suggests c.3 weeks Thank you