How much time do I have to find out what happened to my mom’s stuff?

There's no set deadline. Her "stuff," the tangible personal property in her home, might all be gone already or it might be getting moldy just sitting in the house waiting for someone to do something. I take it you have no contact with any family member. The only thing to do is contact any sibling and ask what is going on.

Since she died without a Will, her possessions would be distributed under the law of the state where she resided. ?There is no time limit, but as a practical matter the longer you wait the less likely you will find anything out. ?Find out who has the property.