Editing Isn't A Once Over
I hesitated to write this because I knew I needed to admit my weakness.
I am not good at estimating deadlines.
There are reasons.
1. I have two small children.
2. I have been subject to my husband's crazy career that kept us moving lots.
3. I don't want to freak clients out about reality.
4. I actually believed for a while I could fit about 48 hours worth of work into the 18 hours I am awake.
As for numbers 3 and 4, I'm getting better at it. But I can only do so much until I learn how to best communicate number 3.
First, there's this thing called spell check, and I can tell if you've run it or not when I run it. Now, I usually go case by case so I'm not blindly accepting changes, but you can usually do this yourself even as a bad speller. See my post about Grammarly.
If you, as the author, have no one else to read it over before you submit it to me, as the editor, then I at least assume you have read it one or more times after you declared it finished. If you have not, you will likely find yourself remembering things that you didn't add along the way, and it will drag out the process even longer once we begin passing the document back and forth.
Also, if you have never read your entire work out loud to yourself, you will be amazed at how much red returns to you on the first few rounds of editing.
So, besides fixing obvious technical errors, what are all these rounds of editing looking at? There is the big picture stuff. If the author spoke about the same sequence of events as if they were new in four different places, we probably need to cut that, at least acknowledging that it had been discussed before or giving new information that makes repeating it worthwhile.
That may need to be a separate read over from where I am correcting the misspelling of a character's name, pausing to look up quotes, getting bothered enough to research if that type of gun can really shoot that far, and other similar issues.
Then, there's manually going line by line through everything for very basic spelling and grammar issues. Misplaced periods, single quotes used where Americans typically use double quotes and vice versa, or the opposite for British English works, and dozens of other errors will be caught.
And just when I think my work is done, sometimes an author, like you maybe, will add or rewrite something. It happens!
Finally when we agree it looks like a complete work... I read it again to catch spaces that accidentally got deleted when we were rearranging all of those words, another variation of a misspelled name I didn't catch the first five times, a repeated word that appeared during some correction along the way, etc. That's proofreading.
And depending on the original state and how many changes have been made, sometimes I proofread it again after I proofread it. I like to proofread it until I find only one or two mistakes in the entire document.
And maybe I will even run Grammarly just to see what it says, in case it catches something - although I'll never trust it blindly, and rest assured if you're paying me to edit, you're getting multiple read throughs by a real person, not just a machine!