At some point there is a need for time estimates, ye. I don't ask contractors for a detailed breakdown, just the whole thing. And they either do a high padded

At some point there is a need for time estimates, ye. I don't ask contractors for a detailed breakdown, just the whole thing. And they either do a high padded fixed price or work per hour. A friend who is an elictrician might do 100 similar rooms in a building and they have a detailed breakdown of "time per screw" more or less. So I guess the accuracy depends on the sameness of tasks to do.