Hi Bluebell,
I’m not the best with insects but I do know that there are two Cabbage Whites, Spring and Summer. The Spring variety larva pupate for around 7 – 8 months and hatch out in early spring.
A good clue is which leaves are being eaten. If the leaves close to the heart are eaten its the Spring Cabbage White.
I’m sure others here will give more detailed info.
Don.