status if an application is rejected.

I have been in the US for about a year now. I came as a temporary visitor when my son met with an accident.I was granted an extension for six months. I wish to apply for a second extension of my visitors status as my son still needs help and cannot manage alone. I want to know the following.

1. If my second application gets refused, in how many days will I be expected to leave the country?

2. If my application gets refused, will the period of time that it took for the refusal letter to come, be counted as an overstay?