Answer
$20 century *0.001s/century=0.02s$
$0.02s/2=0.01s$
$0.01s/day*365.25day/y*2000y=7305s$
Work Step by Step
The last day is 0.02s longer than first day.
The average day is 0.01 longer than the first day.
Then average multiplied by the number of days yields the final time increased.
