Is Hashem in time?
No, Hashem is not "in everything" - that would make him physical. Hashem himself is not inI creation - physicality cannot contain Him. See the Rambam at the beginning of Hilchos Yesodei HaTorah, where he describes that all of the creation emanates from Hashem and if you could God Forbid imagine that Hashem would not exist, all of existence would cease to be. But he is very clear that Hashem has no body, and if you says that he is "in everything," and you mean it in a literal sense, then you are saying that he has a body. This is a terrible misconception.
The Rambam also says in halacha 11 there that Hashem exists outside of time.
I think some rishonim including the Ralbag held that Hashem existed within time but I can't remember where he says this.
Hashem is completely incorporeal, and unchanging. According to the Rambam, Hashem is outside of time, the idea of His existence within time makes it possible for Him to change, and is a compromise of his incorporeality. This is part of what is meant by 'Hashem is one'.
As it relates to creation, Hashem is outside time when man is looking backwards at creation, however, Hashem is within time only if you look forward at creation from Hashem's perspective.
There's sort of a paradox depending on how you're looking at it.