I think this is one of those things that varies greatly from woman to woman. Are you familiar with the normal fluctuations in your cervical position in relation to your cycle? I ask because until I started to TTC, I surely wasn't. I think most women have the SHOW for 3-4 days a month before cervix returns to the low position. Again though, I am sure this is highly subjective. I have been reading TCOYF and doing some research, and from what I can see, a high "closed" cervix is a sign of pregnancy, but does not always occur right away.
So, a wishy-washy answer at best. HTH