之际, 之余, 之下 — three phrases that close with 之

规则 …之际 = at the moment of, on the occasion of — a significant POINT IN TIME: 新年之际…
…之余 = besides, in the time left over from — the REMAINING TIME: 工作之余，他喜欢画画。
…之下 = under, given — a CONDITION or an influence: 在老师的帮助之下…
All three follow the noun phrase and close it; none may precede.
之中 = among, within: 三人之中，他最高。