First of all, I agree with Stuzilla’s recommendations.
10hrs per week is what the experts say is an ideal amount of minimum, strapped-in hang time (that doesn’t include rest time). If you don’t spend that much time hanging, then it might eventually limit your gains (at some future point). By hanging 10 hours per week, you’re giving yourself a better balance of time vs. amount of weight used (since you’re spending a little less time hanging, you’ll need to use a little more weight, and guys usually find their gains slow down around 20lbs or 25lbs). In other words, you want to try & gain as much as you can at the lower weights—and by using more hang-time you can stay at lower weights longer (but still keep reaching fatigue daily).
Let me qualify this by saying, at 4x sets per day, I think great gains are most definitely within reach. You’re getting about an hour a day of strapped in time; that’s not bad (you’re getting 7 hours per week assuming you hang daily). This is especially true if you’re also getting daily split sets. I’ve seen guys make great gains with only 1x set per day (although people tend to peak much, much sooner with lower numbers of sets; i.e. people plateau early if they don’t use enough sets).
Just make sure you’re consistent about targeting the same angle so you get enough fatigue to cause deformation. Also, you’re not doing too many sets, so you probably want to reach fatigue during your first set each day (i.e. get to the point where you feel a need to reduce the weight). Reach fatigue daily (during your first set if possible), then ride it during your subsequent set(s).