From the date of service of summons.
After the completion of these 20 days, the plaintiffs can request the court for a default judgment. The time does not start clicking from the date of filing of lawsuit. The summons does not have to be in any envelope. I am surprised they just left at the door. You can also challenge the service of summons, however, once you receive it, more than likely you are served. Now, the hard part. Was this a lawsuit for collection of money? No big deal here, you can file an answer within 20 days. If you don't have the technical knowledge, our law office can help you in representing this case. We can also do settlement, or file bankruptcy in the alternate. You need to move quickly because inaction would be no good as this would give the other party a free hand in the form of a default judgment and later collection, garnishment or execution of any kind. Call or meet us for a free advice. It is always good to talk to a knowledgeable attorney in these matters. Once you get a judgment, it become difficult to get it vacated as this would also be reported to credit bureaus.
Only see a licensed attorney before you make any decision. This answer may not be perfect in any given situation. However, more fact may be required by your local attorney. If you are in Las Vegas, you are welcome to send your questions regarding Chapter 7, or 13 to Attorney Malik Ahmad at Malik@lasvegaslawgroup.com or www.fastbankruptcynevada.com or by calling (702) 270-9100. In many cases, we do not charge initial consultation fee.
In general, most States' laws hold that the statute of limitations begins on the day that the Summons is properly served. You should speak to a local attorney to confirm that you have a complete understanding of your legal rights and obligations.
Good luck with your case!