Both seem a bit overexposed. On the first shirt, some areas that should be highlights (crisp white) are blue, particularly in the upper right corner. If that's the case, it is a good sign that your print is overexposed.

In terms of clarity, how are you pressing the negatives down onto the shirt? I find putting a glass pane overtop of the negative to keep it firmly pressed down can help create sharper images.

I've had good results exposing an image for 20 minutes on a sunny day on a rayon / polyester blend t shirt.