Your chances of a quick release will depend on what treatments the Dr. has in mind. If it is just to get IV antibiotics, 2 or 3 days to get levels could be enough (but it still just depends on how it works out). I think your first step is to get an exact list of what treatments are planned for the stay and go from there. One bit of advice: get admitted at the start of the week because it is tough to get released on a weekend.