My guess is that they're looking to see if you complete it in a reasonable time period, your initial draft is at least in the right ballpark (anyone experienced in tech support, team supervisorship, project management, etc can answer common emails almost by reflex) and it appears to be you, and not someone helping you.

I would imagine that, if anything, seeing you pause after an initial draft, adjust some grammar and tone, pause...even re-write a sentence or paragraph - and then say "done"...would impress, not detract.