In German predicates sometimes do not consist of a verb only, but of more words. So,
- offen haben = to be open
- geschlossen haben = to be closed
can be thought as one term. If you want, think of it like of a separable verb that even is separated when the prefix stands immediately before the core.
- inseparable verb (handhaben = to handle)
Otto handhabt heute eine Maschine.
Otto wird morgen eine Maschine handhaben.
- real separable verb (anhaben = to wear something)
Jürgen hat heute einen Mantel an.
Jürgen wird morgen einen Mantel anhaben.
- pseudo separable verb (offen haben = to be open)
Das Geschäft hat heute offen.
Das Geschäft wird morgen offen haben.
The translation of
Die Bank hat am Samstag geschlossen. = Die Bank hat am Samstag zu.
is
The bank is closed on Saturday.
but closer to the German meaning are these variations:
The bank has closed on Saturday.
The bank holds closed on Saturday.
The bank keeps closed on Saturday.
addendum (tense and time)
The fact, that the word geschlossen can be both, an adjective and a participle, can be confusing here
- participle
Tom schließt das Tor. (Präsens)
Tom schloss das Tor. (Präteritum)
Tom hat das Tor geschlossen. (Perfekt, built with a form of the auxiliary verb haben and Partizip II of schließen)
- adjective
Das geschlossene Tor lässt sich nicht öffnen.
So, I will use the adverb "zu" now instead, because "geschlossen haben" and "zu haben" are synonyms. This also means: In all of the next sentences you can replace "zu" with "geschlossen".
And now we can vary tenses:
Präsens: Die Bank hat zu.
Präteritum: Die Bank hatte zu.
Perfekt: Die Bank hat zu gehabt.
Plusquamperfekt: Die Bank hatte zu gehabt.
Futur I: Die Bank wird zu haben.
Futur II: Die Bank wird zu gehabt haben.
So, the grammatical tense of "Die Bank hat zu." (and therefore also "Die Bank hat geschlossen.") is Präsens.
But German Präsens does not necessarily mean, that something is happening now, in the present time. This of coarse is the main usage of Präsens, but there is more.
- Präsens can mean the present
on the phone: "Danke, mir geht es gut. Bei uns regnet es gerade."
- Präsens can mean the past
Als Martin Luther im Jahr 1517 seine 95 Thesen verkündet, ahnt noch niemand, welche Folgen das hat.
- Präsens can mean the future
Ich fahre morgen zum Baumarkt und kaufe dort eine neue Säge.
- Präsens can mean any time
Dreiecke haben drei Ecken.
So, you very often use temporal modifiers like "heute, morgen, gerade eben, jetzt, schon bald, letzten Sonntag, kommende Woche, ..." to make clear which time you mean.
"Am Samstag" is such a modifier, but it is ambiguous. The most likely interpretation is next Saturday. In this case the sentence "Die Bank hat am Samstag geschlossen" says something about the future. (But its grammatical tense still in Präsens.)
Another interpretation is, that you mean every Saturday. Then the sentence talks about the past, the present and the future. But for this specific case we have the word "samstags". It explicitly means "every Saturday".
Die Bank hat samstags geschlossen.
But still "Die Bank hat am Samstag geschlossen" also can have this meaning.