The understanding I chewed on and hungrily swallowed from my Gestalt therapy training back in the early 1980's was then, and is today, that gestalt is a here and now experience. Which is to say that gestalt is a timeless experience.
That said, every impression (contact) is a constantly refreshed first new impression; really then, the contact becomes an awareness of the energy of that contact. The Gestalt field is not inherently static, but affords a wholesome dimensionality which is absolutely dynamic.
For example: A butterfly flapping it's wings excites a ripple of energy (awareness) which, in theory IS (and/or) COULD BE within my awareness because the field is that of a complete whole encompassing all. My difficulty is my being able to descern that the butterfly flapping it's tiny wings is the awareness that my awareness is making contact with since I am also, at the same time, being aware of an infinity of other contacts.
My Gestalt training explains to me that since I am always aware of "something", then that "something MUST actually be nothing more then really the field itself. So then, for me to descern or focus my awareness I must bring to my concentrated awareness (my foreground) a figure which emerges from the field (my background) even though the entire experience is still completely within the "infinity bounds" of the whole field anyways. So then, if I am gestalt aware enough, I could find the figure of the butterfly since it is part of the field, and so am I; I have just only to become aware of it as being something that I am not generating into the field, and then start chewing until I taste what I am aware of as a butterfly flapping it's wings.
Now then, once I manage to taste and reject until I swallow the butterly awareness it can easily be understood as a first impression of such an experience in gestalt "thinking". The thing about gestalt is that while I am searching for the butterfly awareness I am also searching for an infinity of other awarenesses. So then each awareness which I don't spit out becomes part of my "new whole" and thus I am constantly in dynamic change. So then, even if I keep tasting the butterfly, MY awareness of the butterly is changing as is the awareness of the butterfly itself. Indeed the whole field changes as I become aware of each awareness.
So what does this all mean? Well simply that every "first impression" (as I think you mean it) can ONLY be a first impression. Second impressions do not exist in my world. I live moment by moment. Everything is always a new first.
What I was before I wrote this post is no more. What I am as I write this post can not last. What I will be after this post is posted would never have been unless I wrote this post. I know it sounds strange talking about the future in the past tense, but such is the paradox of gestalt therapy. (And dare I say it, gestalt therapy theory. At least the way I was trained.) Gestalt is always a beautiful way of living firmly planted in the ground of this both sad and happy mudball; and not flying off course into outerspace to simply enjoy counting the stars. Still though, such a trip does invite me most seductively at times. Well, in Gestalt I guess I kinda do take for the stars anyways. Coming back can be the hard part. I think I come back only because a new me can shoot for the stars all over again.