Unless the specific statute to which you refer states otherwise, the 10 days starts the day your receive it, but that means you count from that day, as if that were day "zero" or "0." So the first day to respond is the next day (e.g. if you received it on Monday and had one day to respond, your response would be due Tuesday), etc. Count 10 days from the date you received the document: if received on the  20th, you would have to respond by 20 + 10 or the 30th.