Question Author
Now I've been given the answer that's partially correct but it came up incorrect on the spreadsheet.
For anyone interested, apparently we gain 11 minutes and 15 seconds per year, despite leap year adjustments, which is why there is no leap year at the turn of the century, other than if the year is divisible by 400 (e.g. 2000)
So the answer was 45 minutes!
I have to say I wouldn't have got that in a month of Sundays with or without any adjustments!!!