Unfortunately, without having done the same job, it's hard to evaluate the time, even if you pad. And for lots of complex jobs you have skeleton in the closet,

Unfortunately, without having done the same job, it's hard to evaluate the time, even if you pad. And for lots of complex jobs you have skeleton in the closet, meetings upon meetings, extra management to contact for approval. I'd rather charge by day/week to discourage those unproductive things and have the company get its act together in terms of scope/approvals so that there is no blocker (or they get expensive).