Search within a specific timeframe

Hi- 

I'm currently searching within a box folder, but for some reason it's not returning the most recently uploaded file? 

Here's my query:

items = client.search().query(query="Query", limit=1, ancestor_folder_ids=["ID"], sort="modified_at")
item = items.next()

It's returning the fourth or fifth file. 

Any ideas on what might be going wrong here?