Punctuation (comma)

[Nordic Bill]

Here's a simple sentence relating to a prediction (of a marriage doomed from the start, a risky business venture, etc.):

"I give them two years tops".

"Tops" meaning "a maximum of".

Question: should one insert a comma between years and tops here or is that unnecessary?

Bill

[Casiopea]

I get at best, a prepositional phrase in form and an adverb in function.

I give them two years at best.
I give them two years, at best.
At best, I give them two years.

[Nordic Bill]

But of course! Why didn't I think of that?! Glad to see the comma is optional as well, which more than answers my question.

Thank you muchly!