Among many other recordings of the impromptus, I have a recording of the op. 90 pieces by Sergio Fiorentino. I can tell you: For these pieces, the guy is unmatched! Listen to his recording and you'll quickly forget the ones by Perahaia, Schiff, Brendel, Richter & co.
The point I want to make here: In the end, it is completely irrelevant if it takes you 4 hours, 4 days, 4 weeks, 4 months or 4 years to learn these pieces. I would take 4 years over 4 hours anytime if, in the end, I was able to interpret these impromtus like a true artist and poet. THAT should be the ultimate goal even though, sadly, it is out of reach for 99.5% of accomplished professional concert pianists (not to speak of amateurs).