Let's say someone falls down and breaks a small bone… like in the wrist. for whatever reason the person decides not to seek medical help, even though he/she is in severe pain.

My questions are:

Would this possibly cause a high fever?

and if so, how long after the bone is broken might the person get ill?

yes, it is possible to cause fever…if tissue damage is high then it may cause high fecer too. the patient may be feverish within 24 hours.