A lot of people ask me how long they should wait after a rejection to requery the rejecting agent.
That timeframe depends on what you'd be querying when you do requery. A new project? A new draft of the old?
If it's the latter, a new draft of an already-queried book, I'd say you should wait at least a year. And in that time you should be revising and using beta readers to figure out how the book can be made genuinely better. We all know my opinions on too-quick revision. (If not, read the #AskAgent archives)
If it's a new project, I say you can requery immediately, so long as the book is ready. Meaning it's been read, revised, read by beta readers, revised, let sit, revised again, and then queried.
A different project, for me, is a fresh start.