How long after using targeted herbicide on an area would you allow pigs on it?

I DO NOT have the pigs yet; I’m trying to decide on a plan for when I get them in a couple months. I DO have an area that does not require herbicide treatment they would be able to live on. I do, however, want to use them to clear a particular area of invasive plants, but the problem is that there is also Lily of the Valley all over it. If possible, I’d spray the LoV this weekend, then again in 2 weeks, and only let the pigs on it in a couple months time.