The absence of specifying when something happens in Chinese I saw this example on another website:
他们都拿着票。

Tāmen dōu názhe piào.

They were all holding tickets.

I noticed that it said they were all holding tickets.
Does that imply it is the past tense?
Or is it a narrative?

If a sentence lacks a time indication is it always a certain way?
Should this sentence include 了？
In Chinese sometimes a sentense may lack a time, which is quite different from English, which has a specific tense. In this case the tense depends on the text and the language environment but not always means a same way. 

For example, imagine that if you were buying a ticket and saw some people who hold tickets, "他们都拿着票" would mean progressive tense. If it is a narrative, it may means past tense.

As for "了"，"了" can be used in many tense.
See this Tense and use of 了