Following an extraction, when will it be too late to bone graft to ensure the best results of an implant?

I had a bottom molar extracted 3 weeks ago.Surgeon said no need to bone graft.As I've learned,whether or not bone graft in this case is not an issue that all surgeons happen to agree on.As I'm weighing my options of preparing for an implant,I'd like to know your thoughts on whether it's too late to bone graft at this point.If not, how much time do I have, after extraction, to still have an effective bone graft?Or should I just wait for it to heal and consider my options in 3 months?Thank you!