The biggest time factor is how complex the work is, and how many strange formatting things happen in the text itself.

For example, each image needs to be placed (essentially) by hand. It's fairly common that people leave italics or bold across paragraphs – and that has to be fixed by hand as well.

The fastest I've gone so far for a full novel is about five hours working straight through – and that was pretty simple (but coming from a PDF). Usually it takes six or seven. Very complex works – or coming from a PDF – takes quite a bit longer. This includes proofing time as well.

Usually debugging is about a third of that time.

My own work, however, is much faster. I know where italics and the like are at, I use RTF already, and so the source document is really clean.