requirements of TD visa

My husband is a canadian citizen, and i am permanent resident of canada. US embassy informed me that my husband needs to get the TN status first in order to apply for my TD visa. But when i called the US border customs and protection , they said thet can't issue the TN visa ahead of time without travelling to US and joining his workplace.they also said that if we can show the supporting documents of his job offer it wouldn't be a problem for getting my TD visa.

i would be very greatful if you can clarify my doubt.

You can get the TD at the same time as the TN or later, but not before. It's a derivative status and tied to his TN. How soon he can get his TN is up for debate and depends on the POE and the officer. The earliest TN that we’ve received is 2 weeks before the start of the job. Others will have other examples. Some POEs do require you to be "on your way".