Upvote:14
There is no "180 day rule". The regulations allow B-2 to be admitted for up to 1 year, but they are usually admitted for 6 months. 6 months is not a particular number of days (months have various lengths), and it matches what you were admitted for -- the period of time from April 9 to October 8, including both the days April 9 and October 8 themselves, is exactly 6 months. In any case, the officer has discretion to admit for a different length of time, so you can't argue with it if they count the months differently anyway.
And yes, if you are admitted until October 8, that is until the end of the day on October 8.
Always check your electronic I-94 to make sure they didn't write down the wrong date.