If you really try to enjoy the game and maybe even search for the hidden collectables 2-3 hours is totally out of the question. If you just want to rush through it - of course - but this is not the kind of game that should be rushed. I still agree that 20$ is too much but I would really say that it's worth about 10$ if you keep in mind that this is an indie title which you can hardly compare with Witcher 3 (which at release had a pricetag of 50-60$ btw).

I bought the game here on GOG using the (afaik still active) special offer of getting it alongside Inside. Inside, again an indie game, also is not very long and has usually a pricetag of 15-20$ so paying 20$ for both games imo is reasonable. I say it again: both are indie games and the pricing eith indie games is not as easy as with AAA titles. If they would set a pricetag of 3-5$ they probably could not exist any longer and at least I would really see another game of those devs (both Inside and Little Nightmares). These games might not be very long but they are just very well made.