Welcome to the TrueAchievements walkthrough for the Twitch app! Here, you'll be guided through how to obtain all of its achievements as easily and efficiently as possible.
N.B.: Always remember that you can snap the stream you're watching and even mute it. It will still count as progress towards achievements while you play another game. This is especially useful if you're watching streams you wouldn't normally enjoy watching or listening to.
First things first, you'll want to keep an eye out for major gaming events that are likely to be broadcasted on Twitch and are very likely to garner more than 100k viewers on a single channel at a time. Notable examples of such events include AGDQ (beginning of January every year), E3 (mid-June every year), SGDQ (end of June every year), PAX events (PAX, PAX East, PAX South), RTX, or when a majorly anticipated game has just been released. Other events also include MLG/eSports tournaments for games like League of Legends, DotA 2, Hearthstone, CS: GO, CoD, etc. Even if none of those particular events are happening close to the time you read this, there may be a channel that's inexplicably at more than 100k viewers, so remember to always check in on the top channels.
Once you do find a channel with more than 100k viewers, simply enter the stream and you'll unlock:
Next, you'll need to search for channels that have fewer than 10 viewers. You can usually find channels like this that will stream for a few hours at a time on single-player story-based games (e.g. Bioshock Infinite, Bioshock, Bioshock 2, Dishonored, Metro 2033, Metro: Last Light, Half-Life 2, Watch_Dogs, etc.). While streams with fewer than 10 viewers can be found in nearly any game, games like the ones previously suggested mean that the person playing it is more likely to stream continuously for a few hours, instead of other types of games where the streamer might play a few matches/rounds/games of something, then stop streaming after a relatively short amount of time.
After having watched a total of 1 hour of streams with fewer than 10 viewers, you'll earn:
HipsterWatched 1 hour of live video on Twitch channels that have less than 10 viewers.

As well as:
NewcomerWatched 1 hour of live video on Twitch.

You'll need to watch 10 hours of streams with fewer than 10 viewers. Once you do, you'll unlock:
Talent ScoutWatched 10 hours of live video on Twitch channels that have less than 10 viewers.

As well as:
Note that if you're unable to unlock the achievement for viewing 10 hours of streams with fewer than 10 viewers, in one day (which is likely), go to the "Monstercat" channel and leave it on overnight (you can turn your TV screen or computer monitor off) to make progress towards the remaining achievements.
Now, essentially all you have left to do is grind out the remaining 90 hours of viewing channels and you'll unlock all of the remaining achievements along the way by watching at strategic times. I'd highly recommend using the "Monstercat" channel; it will be your bread and butter. It's a 24/7 stream of good EDM (Electronic Dance Music), and it hardly ever goes down (and if it does, it's only momentarily; though this is a very rare occurrence). Note that you can always mute the stream (whether you're watching inside the app, or in snapped mode), if you don't want to listen to it, or if you dislike EDM. Monstercat is one of the best channels to use for the purposes of getting all the achievements in the app as quickly as possible, simply because it's one of the most reliably stable streams.
What you'll want to do is constantly view the Monstercat stream. When you're ready, start viewing it. You can snap the Twitch app and view the Monstercat channel while playing other games during the day and it will count. At the end of the day, go full screen with the Monstercat stream and leave it on overnight. If all goes well, the next morning you should have earned:
Max BandwidthWatched a single channel on Twitch for more than 8 hours consecutively.

Keep watching the Monstercat stream the next day, snapping it if you want to play other games. Depending on when you started watching it the previous day, at some point during this day, if you've been making sure to constantly view it, you'll unlock:
Around The ClockWatched a minute of live video on Twitch, in every hour of the day.

That night, make sure to leave it watching the Monstercat stream. At some point between 1 AM and 5 AM this night, you'll unlock:
Night OwlWatched 5 hours of live video on Twitch between the hours of 12am and 4am.

The third day, make sure you keep watching the Monstercat stream all day to constantly work towards 100 total hours of viewing streams. That night, assuming you've been constantly watching between 7 PM and 11 PM the two previous nights, you should unlock:
Prime TimeWatched 10 hours of live video on Twitch between the hours of 7pm and 11pm on a weekday.

Now, the only thing you have left to do is grind out the remaining 40 or so hours. You can choose to keep watching Monstercat for the next 2 days as you've done for the past 3 days, or you can choose to go at your own leisurely pace, watching whatever channels you want, whenever you want. Either way, once you accumulate a total of 100 hours of viewing streams, you'll unlock:
You've just completed the Twitch app! Congratulations!