There are 2 589 420 Facebook users in the Singapore. They each spend 38 mins and 46 secs on Facebook per day making Singapore #1 in terms of time spent per user (Can't reference this off-hand).
United States has 155 701 780 users. All the Facebook users from the US spend a total of 100,000 years on Facebook each month. American users spend an average of 6 hours and 33 minutes on the social network each month.
Normalize:
38 mins and 46 secs user/day = 2326 seconds on Facebook user/day
Total for singapore:
2326*2589420 = 6022990920 seconds singapore/day
6022990920 / 86 400 = 69710.5 days singapore/day
69710.5 / 365 = 191.0 years/day
191.0 * 30 = 5730 years/month
The US has 60 times as many Facebook users so if Singapore had the same population, Singaporeans would spent a total of 343,800 years/month over 3x as much as in the US.
Sanity check:
US (23580 seconds / month) / 30 = 786 seconds on Facebook /day, about 2.9 less time.