The pact itself was announced almost immediately after it was signed. However, what was announced was not the entirety of the pact. Here is the full text:

http://www.fordham.edu/halsall/mod/1939pact.html

It was shocking for most observers at the time that such a pact would be signed. Of course, the secret provisions would have been even more shocking I imagine. The full weight of the pact was understood when the Soviets invaded Poland from the east.