If you are going to work an 11pm-7am shift on a sub-acute rehab, the pace is definetly going to be slow. Most of the time when you begin your shift you won't have many medications to give. You can pretty much thoroughly assess each patient and get your charting done within a reasonable amount of time. After the patients fall asleep, the time tends to go by pretty slow, although you will have a few patients who will use their call lights for assistance to the bathroom.
Daylight shift is another story. I've had up to 7 patients before (even during nights) and half of the time there is no nursing assistant. There is a rush to do your med passes and make sure that your patients are ready to attend therapy on time (physical, occupational, speech, and adls).
As for the managability of a sub-acute rehab unit, patient's have to be considered "stable" to attend three hours of therapy. These patients will come in with deconditioning or post-op status (total knee, hip, back). A good number of them will have numerous other medical conditions such as diabetes, obesity, respiratory/cardiac/GI issues as well as psychiatric. However, don't expect to work too much with IVs, PICCs, blood, tube feeds, bladder irrigation, and all of those other things you've seen on a med surg unit. Nonetheless, these patient's still require more care, so imagine having a total of 13 patients on your unit, only 2 RNs, no nursing assistant, and having to get these patient's ready for therapy, transfer them in/out of bed without a nursing assistant. This is typical on my unit.
I see no reason for you to not have oriention, but that's a good question to ask the unit director. One thing you will definetly learn how to do on your rehab unit- if it is done- is FIM scoring (Functional Independence Measure). If you get the job on the rehab unit, just use it as an opportunity to improve your organization, prioritization, medications, assessment and communication skills.