Is it going to take more than two hours?

Is it going to take more than two days?

Is it going to take more than two weeks?

Is it going to take more than two months?

Is it going to take more than two years?

If you can answer these questions, you can estimate using a confidence interval.

If the estimate is too wide, break it down into smaller chunks, and re-estimate.

If you can't break it down further, decide whether it's worth spending time to gather information needed to narrow the estimate or break it down. If not, scrap the project.