The concept of memory is a tad different for a creature who lives across every instance of time. 

While for us memory is "remember what happened in $\mathit{Life}(t-x)$ while we live in $\mathit{Life}(t)$, for your creatures memory is simply "be aware of every value of $\mathit{Life}(x)$ in its entire dominion.

So, let's say John Doe was born in 1965 July 11th and died in September 2010 November 4th.

The time spread John Doe's "memory" would simply contemplate each and every moment of its existence in that time span, like we see a segment made out of all and every points belonging to it.

By the way I don't think that

> a creature who exists parallelly across every instances of time 

qualifies as 5 dimensional creature.