I revise for months, starting with the day after I type THE END, while the story is still hot on my brain. The first time through usually wipes clear the obvious typos and adverbs, and allows me to pull out the thesaurus rex for boring words and overused words.
The second, third, tenth times through are for getting the not-so-obvious typos (there, their, they're), as well as haggling over paragraphs, re-working them, eliminating a lot of others, and basically moving scenes to better spots. I also continuously look over the first chapter (especially the first ten pages) to make sure it's the best I can make it.
When I finally don't find anymore typos, am satisfied with every paragraph, and am overall just sick of looking at the story, I put it aside for a month. When I get back to it, another two or three passes gets it to where I want it. I use the month off to research agents, work on the query and synopsis, so that after I finally finish the editing process, I'm ready to contact agents.
Time-consuming and anal, but it works for me. So the short answer, sure, dive right into the revising. Just make sure you take a time-out eventually for a final pass. Don't send it out too soon. You'll regret it months later when you re-read your manuscript for the hell of it and see all the mistakes you missed. This ain't a race. It's how you reach the finish line, not when.