Jen, I am very impressed. Your workouts to start are solid
Big thing to pay attention to with weight training is keeping the rest to a minimum to keep intensity up, but enough so that you can put forth a solid effort for each set. So for example, say you are doing lowerbody, upper body, core. Rest between sets, assuming you're not doing a circuit(which is awesome by the way for a change or if you prefer circuit) is like 90 seconds maximum, but thats with high intensity during the sets. If you are doing upper body, maybe a minute, core can recover very quickly once you get conditioned so like 30-45 seconds, or even just the time it takes to change exercises.
Otherwise, I am impressed and am glad to see a good mix of strength and cardio - for your own benefit, doing stuff for balance(even just 1 foot standing around) is awesome as it teaches those ankle stabilizers to fire and keep you upright in the event you step goofy.
So with post partum exercise, its very individual. Many women report it taking a while for everything around the high pelvis and waist line to tighten and tone back, because you have to figure that ab wall stretched quite a bit to accommodate the pregnancy
So the easiest thing to do, with minimal equipment is the basic floor crunch, followed by a plank - the plank which can be modified. These are tougher than a crunch but require a really good amount of stabilizers as well as total core engagement, but you can do a set whenever you like so you don't need to actually dedicate a block of time to it.
So to do a basic floor crunch lay flat on the ground, knees up to roughly 45 degrees, feet flat. Put your hands up so your finger tips are just lightly touching your ears, then the idea is to curl your body up, not into a full situp, but basically so that your upper shoulders liftoff the floor(so its a smaller movement than a situp but engages that ab wall much easier) then control yourself back down - but NOT to the point of resting on the floor, stop just short of that. After 15 good ones, you should start to feel a little burn if you are doing them correctly. The detail here is curling that upper body from flat, and NOT cranking on your neck. http://www.dailyscubadiving.com/wp-content/uploads/2010/01/crunches.jpg
is a good picture of the finished position here though she might actually be able to curl up a hair more.. Minimal rest here, if your abs start to cramp at the top its a good sign that they are actually activating.
For crunches do a big squeeze at the top for a peak contraction of the ab wall. You can probably manage a few sets of 15-30(maybe more if you're more advanced) but you can do them to fatigue, rest 45 seconds, then do another set to fatigue, then a final one, You can also modify these if you wanted to by just letting your legs fall to one side, and doing twist crunches OR feet flat twists(You go alllllll the way up, twist one elbow to opposite knee, return, THEN lower - most people just blaze through these)
Once you get a little burn going, the next thing could be a plank or modified plank shown here - basically the "watch TV" position from elbows and toes. http://sdchiropracticcare.com/wp-content/uploads/2012/03/plank1.jpg
These are actually awesome because they are functional to other things - they require huge activation of the core, balance control, but also the muscles of the upper body and shoulder girdle to control the shoulder blades and arm. These are pretty demanding but the easy enough modification would be to go to the knees instead of the feet. OR you could start maybe on a slight elevation like stairs(head higher than feet) which would also be good for a modified pushup(another functional great) but then progress yourself down.
The beauty of the human body is that if its a 10 horsepower motor to start, if you subject it to a 12hp load, it will over time develop into a 12hp motor. An actual engine would just wear and die out.
The other point to all this is muscles respond to time under tension and full range of motion. Don't just get the reps done to get a number, do them slowly and methodically so the muscle gets the signal that it has to adapt to deal with the stress from the work.
THe other thing is Jen, you can do these ab things whenever you like. And you could do them every other day if you wanted, or on your 4 workout days. Adjusting that diet will lean you out, toning abs and building back that ab tightness simply takes time - it does with everyone. But dedication patience is going to get you there. I am sure you have seen massive improvements with other things in your workouts and diets.
Try these 2 exercises and let me know how these work and I can give you more stuff or adjust some things. I am a big person on functional training, so if it can translate into real life primal movements I tend to prescribe and use it. Life transfers to machines, machines don't transfer to life - right?