Most people have a time in their lives where they have to adapt to a different sleep schedule. Whether you took a new job, are dealing with jet lag, or are just trying to fix a bad habit, it is quite a challenge. If you just try to force yourself to immediately switch to sleeping at the desired time, you may not be able to fall asleep, not be able to stay awake, or have trouble sleeping the exact amount of time.
This is because your body requires a certain amount of sleep on a regular schedule, and if you mess that up, it will naturally need to adjust. If you need 8 hours and only sleep for 4, you will naturally feel the need to sleep for up to 10 to compensate. Likewise, if you oversleep, you may find yourself naturally waking up earlier or unable to go to bed at all when you want. Therefore it's necessary to do the math on what ratio of sleep you need and schedule accordingly. This is not easy to do intuitively. However, I have created the below calculator to tell you what will make your body happy. There are certainly other potential plans, but I have tried to provide the easiest and most balanced methods possible.