As usual and to not change: a certain amount of time, it's impossible to say!
-- Before asking a question: 1° Turn on your brain, your PC doesn't think for you! 2° Google is your friend, the search engine on CCM as well, do a search!
Hi, if you visit sites without videos, images, or sound, it takes forever.
Surfing on sites with text and images, without sound or video, is an average of 46MB per hour of browsing; it can be more or less depending on the page sizes, the number of times per second you change pages... which would mean about 44 hours of browsing on average with 1GB.
For watching YouTube based on the recommended values https://support.google.com/youtube/answer/2853702?hl=en-GB