Hours vary significantly by institution and style of practice. It all depends on how much support you have from residents, fellows, and PA's. Academic intensivists will spend at least 60 hours/week in the ICU, but are usually in the ICU only a week every month or less. Our MICU attendings take q2 call, but are rarely called since the fellow fields all calls. Our SICU attendings are on call every night during the week that he/she is attending. They only get calls on the weekend since fellows field calls throughout the night.
Private intensivists can spend from 40-100 hours/week, depending on the location type and support staff. A lot of busy private intensivists now employ PA's to assist them in seeing patients and performing procedures.
If you work in an academic environment, it is unlikely that you will be performing procedures. These are usually done by the fellows and residents.
Private intensivists may be performing everything from central lines, arterial lines, intubations, tube thoracostomies, to percutaneous tracheostomies and percutaneous gastrostomy tube placements. You will likely be performing para- and thoracenteses on a not infrequent basis.
The ICU setting is full of procedures. I think central venous cannulation is probably the most often performed procedure in the ICU. Even patients who have central venous access established in the emergency department will need new sticks or over-the-wire changes (that's a debate all by itself) if they are in the ICU for a prolonged period of time.
