A children’s book, by Donal Keith titled * The Time Machine to the Rescue.*
Originally published in Boy’s Life Magazine, serially.
Well it is on Amazon, but it’s expensive.
A bit cheaper here.
or
Too dearly-priced for my nostalgia.
My thanks. You get Three Ninjas. 
Got one.
Low cost.
That’s the same author as the Danny Dunn books, right? I loved those as a kid.
Not the same author. The Danny Dunn books were written by Jay Williams and Raymond Abrashkin, and the “Time Machine” stories were by Donald Keith.
Here is a list of all the stories, and I believe the other book is titled “Mutiny In The Time Machine”.Donald Keith (author) - Wikipedia
Other book here:Mutiny in the Time Machine (A Boys' Life Library Book): Donald Keith, Marilyn Miller: Amazon.com: Books