Can I write a referee report too fast? As a math postdoc, I received my first invitation to referee a journal article today, and I accepted the invitation. I've already read a preprint of the submitted article (which has been available on arXiv for a few months and coincides with the submitted version) in great detail some time ago and therefore I already have to say a lot about the article's content and presentation. I was given two months to write a report.
My question, which might be stupid, is now:
Can I write the report &quot;too fast&quot;?
Or, more precisely:

Does it make a bad impression to the editor if I submit the report too fast (say after a week or two)? Since the editor is an influential and important person in the field, I don't want him to think of me as a bad referee, but I fear that he might think &quot;The report came in so fast that the referee clearly did not put much effort into it. I'll better not ask him next time&quot;.

Even if I've read the article before, is it better to &quot;let it sink&quot; for some more time and not rashly send the report to the editor? At what point should I feel confident that the report is ready?


Update: Thanks everyone for the good advice! I sent the report after around 10 days, and it was really appreciated by the editor!
Fast is great! Just be warned that it means editors will like you and send you more requests so you’ll have to learn to say no.  If you also say “no” quickly and suggest alternatives, then you’ll still leave a good impression with the editors.