For the normal person it takes a long time. Quick legacies are created by having a moment to save someones life or making a mistake in front of a huge audience. So we are capable of creating good legacies and negative legacies.
If you want to leave a legacy you have to stick to doing things other people don't like to do over a long period of time. There is a difference between having a profession for thirty years and having a calling for thirty years. A calling requires passion beyond the basics in your work over many years. If you want to leave a legacy as a normal person you're going to have a calling over a long period of time in the same direction. This doesn't mean work at the same place for years on years, it means you need to have something your passionate about and you pursue it on a daily basis over time.
What kind of legacy are you hoping to leave?
Live, love, laugh, leave a legacy.