A search of the following keywords - Alzheimer obsession with time - lead the reader to the following article.
Next, try to expand your creativity and redirect her thoughts away from the obsession.
You want to develop a series of very short explanations -- one or two sentences at most and appropriate to the what is going on at the time of her obsession. For example, if the time she’s remembering is school age children and it’s during the day, then of course they are in school and will be home soon.
If it is later in the day, perhaps they are at a friends houses playing; or, aunt Mary took them shopping for your Christmas present, birthday presents, school clothes, etc.
Whatever makes sense to her (a normal activity at that time).
Remember - SHORT explanation, simple, and matter of fact. Like this is a normal course of events.
Read the full blown article