which sentence is better?

You should plan your post-retirement life in full before you retire from your job.
退休前應該做好
You should plan your post-retirement life in full by the time of your retirement.
到退休之時應該做好
留意呢兩個意思，第一個冇問題（退休前做，大把時間），但第二個其實有問題，因為「到退休之時應該做好」，呢個退休計畫到時係應該已經完成！所以如果要用 by the time，應該改成：
You should have planned your post-retirement life in full by the time of your retirement.

2008-07-01 10:42:27 補充：
不同意樓下所講：

１．retirement 意為 "withdrawal from one's working or professional career" (www.m-w.com)，即係由不再工作呢個事實，post-retirement life 係不再工作（退休）後o既生活。點會係死左？有冇聽過 post retirement planning？如果係如樓下咁解，呢個詞咪等於安排身後事？！

2008-07-01 10:42:40 補充：
２．用 in full，是否一定要已完成而用 should have ...？我只係用 "in full before" 三個字，做左個 google search，取一句為反例：

The Delegate Registration fee must be paid in full before an invitation letter is issued.

呢句係 passive voice，動詞成組為 must be paid，如果轉為 active voice：

You must pay the Delegate Registration fee in full before...

2008-07-01 10:42:44 補充：
可見此中不涉「已完成」呢個概念。事實上我地用 before 時，經常都將事前要做o既事用 present tense 講架啦，如：I can finish this before mom comes back.

兩句句子都該用should have planned，而非should plan，因為句子中有in full這個字。既然是完完全全的計劃，所以一定是完成了，要用perfect tense。

Post-retirement是一個正確的英文字，但是個僱傭合約或福利的字眼，字中retirement是指僱員退休的一天。我認為你句子中的post-retirement是個很中式英文的用法。在僱員一方，retirement通常是指退休後的日子，不是退休的當天。那麼，退休後之後是甚麼？（除了指「大吉利事」的東西，我就想不到了。）我會提議用life in retirement。

至於用plan direct object (transitive)的寫法，我覺得用plan for (intransitive)比較好，因為那是常用法（to plan for retirement）。

第一句的from your job是畫蛇添足，因為retire當然是指從工作退休，不然還可以是甚麼？第二句的the time of your也出現同樣的情況。句子中的retirement當然是指聽者的退休，因為其他人的退休跟聽者該拉不上甚麼關係。The time of亦是多餘的字，因為by接上名詞已經有了在……時間之前的意思。

You should have planned for your retirement life in full before you retire.
You should have planned for your retirement life in full by retirement.

You should plan your post-retirement life in full before you retire from your job.

Becasues 'before' is more resonable for the sentence as post-retirement should be after retirement.

For the word 'by', the plan for post-retirement would be too late as it means you just plan for your retirement as soon as you retired.