YEARS, but I take 1 or 2 out, no one knows for sure .....personally i have always kept my clips loaded, months....no probs.
knock on wood maybe...
I did have an issue with the cheap ACT mags that came with my RIA 1911. They did not lost long. After initial range visits, everything was fine. Loaded up the mags but purchased 4 Wilson combat and 2 kimber mags. Loaded all them, did not shoot again for about 5 months.
The ACT mags both had FTF issues next time I used them. I've never had any problems with any other mags.