Question

2. Only after a long time's argument        on the time of outing (agreement)

很长时间的争论后，他们才就出发时间达成一致。

Answer 1

2. did they reach/come to/arrive at an agreement only+状语位于句首时，句子应用部分倒装形式。 reach/come to/arrive at an agreement为固定搭配，意为"达成一致"。