postpone侧重延期，延缓，如比赛延期等；extend通常指合同期满，延长合同期限。

例：

合同期满后如一方想延长合同的有效期，应在合同期满以前通知另一方。延长的条件由双方协商决定。

If one party is willing to extend the validity of this contract, the Party shall inform the other Party before the expiry and the term of extension shall be discussed and fixed by and between both parties.

They would be very reluctant to postpone or cancel the meeting. 

他们非常不愿意推迟这个会议或取消这个会议。