How Long Must I Wait After Removing my Wisdom Teeth to Start my Impressions?

Usually a few weeks until the socket starts to close over.  If you do it too soon you can cause the loss of the clot resulting in a dry socket.  It may also depend on whether you had a surgical extraction or simple extraction as to how long you may need for healing.  I would consult with the dentists who is taking the impression. 

You should wait at least 7 days before having impressions taken after wisdom teeth removal or any extractions for that matter. The reason is twofold. One of the reasons is what you brought up. A blood clot forms in the extraction sites and this is the first step in the healing process. The clot takes about one week to fully mature. The suction from an impression prior to this will remove the clot nd cause severe pain known as a "dry socket" and will delay the healing of the socket. Secondly impression material can get stuck in the extraction socket and if left may cause an infection. There should be no real reason to have impressions prior to this under normal circumstances. Trust me you won't regret it

2-4 weeks is a pretty standard time to wait until impressions are taken.  Then you can be sure the healing process is underway and that there are no problems.  

We definitely want to take it easy the first 2-3 days after an extraction, especially if you're over 25.  This is another reason why it is recommended to remove them at a younger age, as soon as your dentist feels like it is time.

If the blood clot is dislodged, dry socket and pain usually follow.  This is the body's way of telling us it is not healing properly.  So take care those crucial first few days!