Time estimations by LLMs are hilariously incorrect all the time. It estimates very simple things that a human could do in an hour to take days or weeks and other things that are genuinely tedious and time-consuming it estimates taking a few hours. LLMs have no understanding of time and no world model that even allows them to make correct time estimates. They will always fail to provide decent time estimates unless the task is well-known, in the training data and they can extrapolate that with a simple math script.
My favourite story is of an elderly coworker with no AI experience who innocuously asked GPT-5-mini (at the time his framework's default model) to translate a 50 page engineering spec, and it kept him at arm's length for about a week about how that task would take just another 24-36 hours more. He kept asking like, you finished yet? and it just made up excuses, "so sorry, I got distracted, give me one more day", and he went "please finish, I need this", and 5-mini came back "I totally understand -- let me get to work immediately, I'll report back ASAP", end of conversation. He got annoyed but never even suspected anything wrong, because this is the kind of conversation he's used to. I wonder how long this would have continued, if I hadn't intervened by chance.