By "fulltime" I mean I spend about 40 hours/week in my day job, and about 40 hours per week taking care of my daughter. Breakdown: 1 hour per morning getting her to school, 2.5 hours after work. That is 17.5 hours during the weekdays. I spend probably at least 20-24 hours on the weekend with her on average. (Note that there are 112 waking hours in the week)
However (!) note that I can multitask many other things while taking care of her, particularly chores and yard work (she often plays outside with me while I am doing construction work or yard work). She is also often self-sufficient, and often entertains herself by drawing (we try to minimize the amount of TV she gets). Also (as mentioned in another comment) my wife simultaneously watches her during some of this time so its a bit easier (although as long as she is awake it is near impossible for me to work unless I am out of the house).
About doing a great job: you are absolutely correct. I do not excel at my day job (in terms of putting in overtime), but I am performant enough during my shift to keep them happy. And I do not excel at being a dad, but I consider myself a better dad than many I know, FWIW :)