You are punished for changing the game time (no matter how much, it seems), but not the system time. Here's what happens:
If you change the time on your 3DS system, Animal Crossing seems to simply think that's the time it is now. Trees grow, events change, the only "bad" things that happen would have happened with the flow of time. Even going back in time via this method seems to work okay, even when going to a day previously played.
If you change the game time, using the option at the main menu of Animal Crossing, you will randomly trip for a while after changing the clock. The duration of tripping seems to last longer than the current play session, possibly the full day? But it eventually goes away. If, however, you were to change the game time this way before every play session you would trip randomly every single session, which is highly frustrating.
Also note that going backwards in time will spoil any turnips you had, since the game knows you went backwards, while it doesn't know you went forwards if you go by the system clock.
tl;dr: Change your 3DS's system time to time travel, do not mess with the in-game clock regularly or will will randomly trip.
Unfortunately, there's no way to rotate patterns. Unlike furniture, which will drop in a certain direction based on where you're facing, patterns do not behave this way. They are always placed in a fixed position.
If you have a pattern that's not facing the direction you want it to, your only option is to either remake it if it's yours, or delete it if it is not, as you can't redesign patterns made by other people. Alternatively, you could also make a new, rotated pattern based off of the design of the existing piece by looking at it which, while somewhat tedious, would work for your purposes.
Best Answer
Usage of QR Codes is unlocked at the Able Sisters clothing shop after becoming friends with Sable. If you've played previous entries in the Animal Crossing series, you might be familiar with this process: you simply chat with Sable at least once a day for a number of days, and she gradually becomes more friendly with you.
As far as I can recall, this is the first game in the series that rewards you for going through this friendship process.
Update: I've been speaking with Sable every day for 10 days, and now the QR machine has been unlocked today (which would have made 11 days if I had to continue). I spoke to her for 10 consecutive days, so I do not know if this will also work if you skip a day. Lyle and Nook had a short conversation regarding the Able Sisters when I visited them yesterday -- I'm not sure if the friendship process unlocked that but I think it is probably an easter egg.
At any rate, the QR machine looks like a large sewing machine that sits on the back wall near Sable. When you attempt you interact with it, you will open dialog with Sable.
Instructions to read QR codes are as follows:
The displayed design will then become one of your 10 patterns.