they can go a while. Several weeks. Just make sure the cage is kept clean, fresh water is always available, temperatures are correct, and boost the humidity a bit. (You can mist the cage lightly 1 or 2 times a day) but a Moist Hide Box would be better.
1). Typically, the shed process begins with the snake hiding more than usual.
2). Sometimes they will refuse to eat, but sometimes they will eat.
3). At some point in time the skin will appear dull, wrinkly, loose and you might even see flakes coming loose. (Do not try to peel it off yourself).
4). The eyes will Cloud Up. This is called "going blue" because a snake with dark eyes will appear to be milky blue in color. But if your snake is an albino or has red eyes, they won't necessarily turn blue, they might just look dull.
5). After a few days of being blue, the eyes will clear up and look normal again.
6). The snake will actually shed after all this.
The entire process from start to finish can be anywhere from a few days to several weeks.