Here's a graph of average hours of computer usage per US household in 2009:
https://www.statista.com/statistics/187622/average-hours-per...
Let's assume these figures are useful as a first approximation of the number of hours of laptop usage per laptop owner in 2018. I'm not saying it's a perfect match, just that they're likely to be better than figures you or I would pull out of the air.
Taking the centre of each band, assuming "more than 10 hours" means "10 to 16 hours", and excluding the "no computers" band, gives a mean of 4.3 hours per day. So each laptop is active roughly 18% of the time.
That's more than I expected, but it still means you're going to need a lot of people to pin the content before you have a 99% chance of at least one copy being online at any given time.
Edit: As far as I can tell, with 18% uptime you need 15 copies for 99% reliability (assuming no correlation between the online times of the various copies, which is optimistic - in reality there will be strong daily and weekly cycles).
(around 65% of Americans between 18 and 50 have PC/Mac laptops- see https://www.statista.com/statistics/228589/notebook-or-lapto...)