Well your routine looks great. Personally I wouldn't stretch her feeds yet as she is so you and sleeping well.
Is it literally 2 or 3 mins she is feeding for or could it be 5-6mins? They do get much more efficient at feeding as the approach 3mo so it could just be that she is done and getting enough. Mine were both down to 6 mins total for most feeds by your DS's age.
It could be that she is more tired at the WU and BT feeds and that is why she takes longer to feed. And the for morning feed she is probably very hungry when she skips the 4am feed.
Do you have a feeding pillow at all? I find mine invaluable even feeding a 1yo. It allows him to lay perfectly horizontal at the right height to feed with little effort from me. I always struggled getting a good position without it. I have a Widgey one which I love since it is overstuffed and so supportive. Some of the others I tried weren't high enough and not as firm.
Could you have an overactive let down that means laying down makes it easier for her to feed? Just an idea in case none of the other things I've mentioned grab you.
It doesn't sound to me like she isn't getting enough to eat at all. Well done mama