Hi! So this depends on whether you want to submit for official critique or community critique. Either way though, Lesson 1 and the 250 box challenge (I assume you have only finished these two) are only two submissions, you are supposed to submit all of the exercises in the lesson at once.

If you are planning on submitting for official critique, you will need to submit all exercises in lesson 1 and wait for feedback and the 2 week waiting period before submitting for the 250 box challenge. In addition, due to how lessons and challenges build upon previous ones, you will need to do additional (I believe 50) boxes for the 250 box challenge before submitting that.

For community critique, there's no restrictions on submission, so you can submit everything at once if you want. But the fact that the lessons and challenges build upon previous ones still apply, you may have to redo some exercises or parts of the challenge if there are some issues with your approach. Also, note that community critique is not guaranteed, so you may have to move on to later lessons even without feedback.