How long of a gap should I leave between using crest white strips and getting my teeth professionally whitened?

There is no need to wait between using Crest Whitestrips and any kind of professional whitening. The only concern is if you experience sensitivity, you may want to wait until the sensitivity subsides. You can also use Sensodyne toothpaste to help with sensitivity during the whitening process. There is no harm to the enamel.

Hi:There should be enough time in between whitenings for the sensivity to completely go away.  This varies in different people.Best,Dr. Maddahi 

Properly administered whitening will not "erode" your teeth. However, either the materials themselves or the trays used to administer whitening can cause gingival irritations as well as transient symptoms such as cold sensitivity. Additionally, there will always be some form of "chaulkiness" or "blotchiness" from the whitening process for a few days after completion until the teeth re-hydrate themselves. Although these issue are typically minor and self-limiting.. completion one week prior to any major event should be plenty of time. Hope this helps.