Merriam-Webster says about another the following:
being one more in addition to one or more of the same kind
However, I come across such sentences as: “I am giving another three books away”, “give me another 2 flowers”. I think it’s fine to say “give me another twenty minutes” as it is a period of time, but I wonder about “another two books/flowers”. Is it grammatically correct? Another thing which seems to be suspicious is that I can’t find such examples in dictionaries.