Anyway … I've recently been rereading Susan Coolidge’s What Katy Did series of books, which were originally published between 1872 and 1890. They're kids’ books, but still enjoyable to read now I'm an adult. In the fourth book, Clover, Katy is described as having forehandedness and it seems that this is the opposite of procrastination.
Delighted to have found the word I was seeking, even if it is rather archaic! Have a great weekend.