Please help! I'm trying to maintain my masters position until the end of the season. I'm confused on

I just hit masters 17 LP today and I have a few questions about what I need to do exactly to keep masters until the end of the season (nov. 11). I am trying to sit on my LP until the end of the season so I can get my masters border for next season. However, in masters you can only wait 10 days and then your LP starts to decline.

1st question: I am confused by what exactly "10 days" means. Example: I just played a game today, so in 10 days I will start to decay. 10 days from now is November 1st. Is it at 12:00 a.m. on nov. 1st that my LP decay will start and if so for what time zone? Or, is it counting 24 hours per day times 10. Which means the exact time I played was at 8 a.m. so nov. 1st 8 a.m. my decay will start. Which one? I feel like only riot will know, unless there are players who are familiar with the system from previous seasons.

What I'm trying to do is wait 10 days from now and play 1 game so it resets my LP decay for another 10 days which should be the end of the season. I'm trying to figure out if I need to play 1 game or if I will have to play 2 games. If I have to play 2 games, lets say I lose both. I'm starting a 17 LP. After the first loss I'll be at 0 LP. Now, if I lose while at 0 LP is that going to demote me to diamond 1? I just hit masters like 3 days ago played 1 game today and lost, didn't demote. Played another game and won 17 LP. I feel like I shouldn't demote after losing 1 game at 0 LP. What do you guys think?