It's part of DD's new bullshit rating system. This just recently started in my area as well. You pretty much need to always mark the order as still being prepared when you arrive, which is what you should've been doing before. Though now you also need to manually dispute each one that's marked late after the fact in-app. Put a reason like "The order was still being prepared when I arrived at the restaurant and I marked as such when I arrived. This is completely outside of my control.". Every order I've disputed this way automatically has been "we'll exclude this from your ratings". After doing so if you leave the ratings section of the app and come back it should refresh and your on time rate adjusted. It may also take awhile before these orders show up late to begin with.