When a short prepositional phrase is a simple adverb, it is never punctuated based on essential/nonessential. When it is an adverb, it usually takes no punctuation since adverbs get to wander around in the sentence.
...On Monday we visited her in the hospital.
...We visited her in the hospital on Monday.
...We visited her on Monday in the hospital.
There are times when a prepositional phrase is very interruptive and needs commas for readability.
Happy punctuating!
Margie