I have some time zero prints that have been kept in the dark - a filing cabinet - that are 15-years old. They seem fine. I have another couple of SX-70 shots that are more than 20-years old (not sure if that was time zero or the older SX-70 film) that have been hanging in normal room light (no direct sun) under plexiglas - they look fine to me.

I have other prints that are about 10-years old that have begun to yellow in the white areas. I know that the film was nearing expiration at the time I made the exposures. I think that's the reason for the discoloration. 10-years ago, I could still buy the film at Walmart and Kmart, but the stuff sat on the shelf for a long time.

I'd be sure to get fresh film, but as Ann says, the newest batch seems bad for manipulations.