I know that backshifting can used when reporting statements and questions. This is clearly stated in many grammar books. Aside from a mere example on some webpage, I haven't found any reference in the authentic books and websites I've checked that I could use as a proof that backshifting can be used in reported imperatives and requests with complex time clauses.
If backshifting can be used what is the rule for using it in the imperative and request sentences? Always used? depends on whether the reported situation out-of-time or not? never used?
The following is some sample request and imperative sentences with reported speech as I see it for the first two sentences. Pronouns are not important. Choose as you see fit.
Can I come back again when I find my book?
I asked her to come back when I found my book.Come back when you find your lost keys
He told me to come back when I found my lost keysShutdown the computer before you leave
Do exercise 10A after you've finished this one
Tidy up now if you are leaving tonight
Best Answer
Can I come back again when I find my book? I asked her if I could come back again when I had found my book.
Come back when you find your lost keys. He told me to come back when I had found my lost keys.
Shutdown the computer before you leave. He told me to shut down the computer before I left.
Do exercise 10A after you've finished this one. She told me to do exercise 10A after I’d finished that one.
Tidy up now if you are leaving tonight. He told me to tidy up then if I was leaving that night.