"The elimination
half-
life of
gliclazide varies between 12 and 20 hours" (Gliclazide being the generic name for Diamicron, which is also a slow-release version of the medication)
Info from here -
https://www.medicines.org.uk/emc/product/1321/smpc
"Half life" means the time the med is active in your system, although the effect will lessen towards the latter end. You could maybe check how long
"Januvia has a half life of
12.4 hours, and so after
87 hours (about 3 and
1/2 days) greater than 99% of the drug will be out of your system. There are several other classes of medication available for the treatment of diabetes"
This seems the general opinion, although I know very little re Januvia. There are several references in Google, of which this is just one.
https://www.rxlist.com/januvia-drug.htm#dosage
I'm not a medic and I'm not saying any of this info is accurate but it does seem to generally say same.
At least it should give you a starting point, should you wish to delve deeper. Alternatively, ask your pharmacist as they will either know, or be able to check, for you.
So, the suggestion of a biscuit, ie Rich Tea, but not a high sugar content, should do you OK without raising your blood levels too much.