Life.

So, I have just turned 66. I hope to live to 90, so that gives me another 24 years.
24 years  at 365 days/year at 24 hours/day gives me 210,240 hours left to live.

But I expect to sleep for 8 hours a night (I hope) so that reduces my available lifetime by
8 x 365 x24 = 70,080 hours.

 Equals about 140,000 hours left to live.

I had better get on with it.