In 1965, Polish artist Roman Opałka hung a 196 × 135 cm canvas in his Warsaw studio. In the top left corner, he painted a tiny numeral 1, then a 2, and so on until he had filled the canvas with numbers. Then he put up a new canvas and continued where he had left off.
He called these images "details"; all of them had the same size and the same title, 1965 / 1 – ∞.
He vowed to spend the rest of his life on the project. "All my work is a single thing," he said, "the description from number one to infinity. A single thing, a single life. ... The problem is that we are, and are about not to be."
At the start, he painted white numbers on a black background, but in 1972 he began gradually to lighten the black with each detail, saying that his goal was "to get up to the white on white and still be alive." He expected that this would happen when he reached 7777777 ... but at the time of his death in 2011, he had got only as far as 5607249.

Your tasks:
1. How many digits are there in Opałka's "Details"?
2. On what date he painted the canvas including 3333333?
3. On what date the last number?
4. What is your estimate of total amount of working hours ?

FACTS: 1 to 35666 (1st canvas completed in 1965): started with brush and color, later b&w with pinceau #0
Canvas containing 3431681 to 3546420 completed in 1970
Output per year was decreasing at a certain rate till 1972, then the output slowed again.

Make your own assumptions regarding missing data (such as hrs/day, days/week etc.) Not much is available on the web.