Teaser 2968: Gardening division

From The Sunday Times, 11th August 2019 [link]

George and Martha’s garden is a perfect square of length (whole number of metres) a two-digit number AB. The area is a three-digit number CDE. In the middle, they have planted a square flowerbed of a length which is a single-digit number F and area a two-digit number GH.

They have called in a gardener, who works for a single-digit I hours. He works for a whole number of minutes on the flowerbed and the remainder on the surrounding lawn. Each square metre of the flowerbed requires N (a single digit) times the time spent on each square metre of the surrounding lawn. I have mentioned nine letters, A-I inclusive, and each stands for a different positive digit.

How many minutes does the gardener work on the lawn?