I suspect your browser has the file cached, or is using a proxy which caches the file. I tried downloading a file from youtube and got a similar duration in three different ways.
url = 'https://r3---sn-tt1e7n7e.googlevideo.com/videoplayback?id=o-APMpsV_ubZwYnre71FtKIY7rTKTd1HmAGqjFS7D_W9vO&itag=22&source=youtube&requiressl=yes&mm=31%2C29&mn=sn-tt1e7n7e%2Csn-tt1eln7s&ms=au%2Crdu&mv=m&pl=25&ei=g-LdXNT1H-ODir4P0Jeb0Ag&initcwndbps=2695000&mime=video%2Fmp4&ratebypass=yes&dur=91.649&lmt=1556128078557211&mt=1558045252&fvip=3&c=WEB&txp=2216222&ip=184.75.215.122&ipbits=0&expire=1558066915&sparams=ip%2Cipbits%2Cexpire%2Cid%2Citag%2Csource%2Crequiressl%2Cmm%2Cmn%2Cms%2Cmv%2Cpl%2Cei%2Cinitcwndbps%2Cmime%2Cratebypass%2Cdur%2Clmt&signature=481807C3CAD81BC6CFA6E4131D5E734BC2CB63FC.2EBF166C597725BC02E9EE28227B9A9C815E224C&key=yt8'
import urllib.request
urllib.request.urlretrieve(url,"file.mp4")
import urllib.request
data = urllib.request.urlopen(url).read()
open('out.mp4', 'wb').write(data)
import subprocess
subprocess.check_call(["curl", "-L", url, "--output", "out4.mp4"])
To disable your caches on the browser, e.g. chrome, you can try Disabling Chrome cache for website development