What day is it?

Ok, I'm not THAT far gone, I know it's Sunday however for some reason I feel compelled to know exactly how many clean days I have.  I took my last Perc at 10:30 AM Thurs.; so do I start counting from there, i.e. 10:31 AM Friday starts day 2 or would you consider Thursday a using day so it doesn't count and Friday is day 1.  A subtle distinction, I know, but whatever helps get you through.  All opinions welcome.

Peace,
Kate