There are a lot of different permutations and practice models to the questions you ask and thus, you'll probably get a variety of answers. Likewise it is hard to define an "average day" but I'll give you my broad strokes.
Fellowship: Most places break up clinical and research time 50/50. There are variations to this breakup and within the clinical and research time, there are further variations of month blocks of clinical/research time, versus weeks/days. Most clinical blocks will be PICU, CVICU and Anesthesia with electives and other variables thrown in (practice attending, sedation time, etc.). Most places (I think) have some version of day shifts (6am to 6pm) and night shifts (6pm to 6am). You show up when you are requested to, but you leave when the work is done and patients are stable for handover, as long as you don't break the 80 hour work week and don't take on new patients after 24 consecutive hours. It is impossible to say what that day looks like on average because there are a lot of variables that go into the day (acuity, bed space, admissions, discharges/transfers, family meetings, educational opportunities, procedures). In fact, the absence of the "average day" is what makes the job interesting. Like momma Gump said, "You never know what you are going to get". Actually, the clinical aspects, though there is variability among programs, is pretty standard from place to place. The ACGME regulates this pretty closely and every program is expected to train fellows with the same basic skills to take care of critically ill patients. The research, or scholarly project, on the other hand is highly variable. More so than clinical time, the research time has no typical day because 1) people do lots of different projects and 2) there is no daily time table, so people kinda do with their time how they see fit within the scope of the project. I did bench research and showed up at 8am (earlier than lab mates) and at 5pm or when experiments were finished. Sometimes, I stayed post-call or on my weekends off (though I made sure I never recorded those hours or told the PD. I'm not suggesting other do that, but it was just an example) because I didn't want to get in trouble for going over work hours. Either way, because of the variability in research training, or scholarly projects, the only thing I've observed is that the more effort fellows put into it, the more they get out of it and the more successful they are.
Attending: So, here there are many different models (more so than fellowship). There are academic positions and private practice positions (locums or stationary). I don't work in private practice, but maybe someone who has or does can comment. The typical model I've seen it 2 weeks on, 2 weeks of per month, however I'm sure there is tons of variability to that model. Typically when you are on, you are on 24/7 for the duration of your service time, but when you are off, you are off. The acuity is probably variable depending if your practice is attached to a bigger medical center, or a community hospital. As far as academics go, again variations depending on the track. Typically tracks include clinician-educator, clinician-scientist and in some place master-clinicians. The master-clinicians are essentially clinician only members of the group and don't, or have limited, educational and administrative responsibilities. Their goal is really only to see patients. The clinician-educators see less patients than master clinicians, but more than clinician-scientists, and have the added duty of administrative and education roles (student/resident/fellow education, curriculum development, stimulation training, didactics, student development, etc.) as well as committee assignments, QI development and have to maintain productivity in the those extra-clinical roles. In my experience, a majority of the PICU attendings at academic centers are going to be in this role, but institutions variety. Clinician-scientists usually have the least clinical duties, but because of that, have to supplement their salary with grants and external funding and are typically held to higher standards as far as publication numbers. These attendings typically do bench or clinical research, or a derivation of the two, and in some instances QI depending on funding opportunities available. Again, given the diversity of practice models in academics, there is no average day, it is highly person dependent. Additionally, because in most places, salary is mainly decided by the number of patients you see and not whether you have extra-clinical projects, the degree of involvement in extra-clinical activities varies, typically depending on 1) a desire to get promoted or not fired (speaking to tenure tract) and 2) work-life balance. There are some academic centers that have part-time models, though I haven't seen that commonly. So the average work week could be 24 to 36 hours for some and 80 hours for other, again depending on personal preference of work-life balance, income need, career goals, etc.
There are several other PICU attendings on here that I'm sure could give you their own experience as well.