It is clearly better to engage in asset protection planning before you have any creditor issues. But planning after a lawsuit has been filed -- or even after a judgment has been entered against you -- is frequently possible.
State fraudulent transfer statutes vary in a number of respects. But as a general rule, a conveyance is voidable (i) if there is intent to improperly prevent a current creditor from collecting against you or (ii) if the transfer would make you insolvent. See for example Section 1336.04 of the Ohio Revised Code.
Stated another way, you are not always prevented from transferring assets just because there is a lawsuit or judgment pending against you. For example, lets say that you have a net worth of $1 million and a judgment against you for $10,000. As long as you have no other known creditor issues, that $10,000 judgment does not prevent you from protecting the other 99% of your assets.
Again, it is clearly better to engage in asset protection planning before any creditor issues arise. But trasnferring assets after a lawsuit has been filed or even after a judgment has been entered may, under many circumstances, still be appropriate and advisable.