How long can an aneurysm be there before it ruptures?

Many years: The likelihood that an abdominal aortic aneurysm will rupture is mostly related to how large it is. Most aneurysms develop very slowly over a number of years. Once it hits a critical size however, the risk of rupture outweigh the risks or surgery and therefore surgical repair should be performed.

Depends on size: See cdc.Gov AAA fact sheet. Make sure you keep up with your follow up to make sure your AAA is not enlarging.