Here is a timeline of shiny Pokemon 
So, for all my non-community day shinies, I got:
• 1st shiny Magikarp six months after release
• 2nd shiny Magikarp six months after release (within two minutes of catching my 1st shiny Magikarp!)
• 3rd shiny Magikarp ten months after release
• Shiny Swablu two days after release
• Shiny Pichu seven months after release
• Shiny Wailmer one day after release
• Shiny Omastar one day after release
That is also the timeline of which I discovered them, too. So quite a mix of waiting time there. Quite a long time for Magikarp (then two at once!) and Pichu, but the others within one or two days.
My 24 other shinies are all from community days.