However, I do think it is worth a trial without either now or later.

without 是介词。介词后面按说应该接名词、代词或动名词。然而，本句接的是两个“副词” now 和 later。而 either 和 or 是连接这两个副词的一对连词。

为什么介词后可以接这样的成分呢？

原来，英语为了简练，“成双成对” 的词，不管什么词性，都可以用在介词后。例如：

There is a big gap between rich and poor in that country.（两个形容词）

此外，为了简练，名词前面还省略冠词：

a relationship between husband and wife

a relationship between father and son 

a relationship between mother and daughter 

a relationship between master and servant 

a relationship between teacher and student

from door to door 挨家挨户 

from morning till night 从早到晚  

from beginning to end 自始至终

from south to north  从南到北

我觉得without是副词作状语，相当于without coffee。又如：

If there's no sugar we'll have to manage without.  要是没有糖，我们也只好不用糖就凑合了。《牛津高阶英汉双解词典》