If one way of deciding a work of art's value is the time spent to make it, can it be that an art work made in a rush has some value, because it is done fast in a limited time? That is, the value is not in its overall quality but, it's quality in relation to how quickly it was done? Like a quickly written poem is unlikely to be as good as one re-worked over a long period but, it could be said that "it's not bad, considering the short time it took to write." Judgement of its value lies then in knowing how long it took to write and weighing this against the work.
But, we never know how long a piece of art work takes. We can only guess. Only the artist knows and then only roughly. And, of course, a debate could be had that when doing such a calculation, should training and years of experience be included?
On a similar note, I was at an exhibition of landscape paintings and photos, talking with the photographer when a lady turned from examining his work and said, "They are lovely, but they don't take long to do, do they?" She wandered off to look at the paintings (perhaps to relish the time they took to make). Later, I got to thinking and did a calculation. Keeping in mind that a photo takes preparation and post production (and ignoring all this for a moment), what would be the hourly rate of a photograph with a 1/100th of a second shutter speed if the photographer was to receive £50 if somebody bought it? Well, there are 100 1/100 th of a second, in a second; so that's £5,000 per second, which times 60, makes £300,000 per minute and times 60 once more, comes to an hourly rate of £18,000,000.