Jennnfier, I did ICU nursing for 17 years before leaving for home health. I can tell you, and I worked nights the majority of that time, I worked most of my hours ON MY FEET!! Like Matt said, it can truly vary, depending on pt acuity.
My typical night in the CT ICU recovering open heart surgery pt's was 7-7:30 report, 7:30 assessment, then vitals, I&O every hour. As son as I assessed the pt, took care of any immediate problems, gave any meds due, and wrote up my initial assessment, I would read my charts. In my initial assessments, I always checked for emergency bedside stock, checked and calculated all drips for accuracy and levels, to see when new bag is needed, if meds are needed from pharm before they close, and to see all alarms are set the way I want them, and all are ON. Then, I read the chart, history, physical, progress notes to see what the plan is for the pt, current labs, what ABG's were on room air, normal filling pressures, what the cath lab report looked like, etc... This took me until about 9:30 10p. I restocked the unit, and tried to give the pt some period of uninterrupted rest. During any time MY pt's were sleeping, I would see if my neighbors needed help. I never sat unless everyone else could also sit. Basically b/c if I sit, I get tired, so I keep moving. About 3 am or so, I got pt bathed for day, weighed in bedside scale sling or standing if possible. CXR's were done at 4, labs at 5, rounds with surgeons at 6, removing CT's, ETT's, whatever needed to be done by MD's. Then clean-up, finish notes, leave fresh bags of IVF if due to run out before 9am (in case day nurse gets busy) give report, and adios! After I left that unit, I went back about a year later, as agency, and they were transferring pt's to the floors before 7:30 am if beds were ready. Well, that was it for me. Nights was already very very busy in that unit, and I decided transferring pt's, for routine reasons and not to triage for an emergency bed, was just not going to work for me, and I never went back!
The only time I ever did experience sitting for any length of time was when I worked nights in CCU. There, they like the pt's to get uninterrupted sleep, so as not to stress them out, after fresh MI. Sometimes I would watch 3 pt's sleep all night. I still read charts, prepped stuff for days, helped neighbors, read journals, etc...
If you start in ICU, I strongly suggest you transfer to nights after orientation. Day shift is sooooo busy with transfers, consultants, pt's going to and fro for CT scans, a major ordeal when on a vent, etc.. I felt like I did tasks all day, and was never able to read the charts, or take in the big picture. It was more like survival from hour to hour. On nights, even though I was busy, I had time to read the chart and think about the responses to the changes in therapies, and titrations of drips I made, b/c I wasn't continuously interrupted by the phone, PT, dietary, pharmacy, etc... I had time to analyze what I was doing, and I really really learned a lot. Now I have worked agency in some hospitals where each nurse had 3 pt's who were all circling the drain at once, and we never stopped to open a chart unless it had orders on it!! Just barely able to suction, give meds, turn, etc... Usually if it's a 3 to one ratio in ICU, it is very hard, 3 to 1 on CCU may be better, but cardiac and fresh MI's can be like little time bombs that will go off when you least expect it, and like Matt said all heck will break loose. 2 to one ratio is good, but as a new grad be SURE you will have a free preceptor who is not counted as staff, you should both be counted as one person for at LEAST 6 weeks. Get them to put you in the ICU cource asap. Take ACLS, and read read read, and ask questions!!
Good luck, and go for it!!!