The short answer to this question is: No, as long as your ex-spouse's retirement account is indeed a 401(k). If you have been awarded a portion of your ex-spouse's 401(k) as a part of your divorce, it is very likely that either your attorney or your spouse's attorney has drafted a document called a Qualified Domestic Relations Order (QDRO) which must be accepted by the retirement plan administrator and signed by the judge in order for you to receive your portion of the 401(k).
Once the QDRO has been approved and the order entered by the court, you will receive your portion of the fund. There is no need to wait until your former spouse retires or begins to withdraw funds from the account. However, if the retirement account is classified as another type of account, such as a pension, you may have to wait until your spouse retires or begins receiving payments before you begin receiving your portion. Thus, it is extremely important to determine the exact type or retirement account will be subject to division upon divorce.