Out of Time by Cliff Ball

A scientist discovers time is actually fluid; past, present, and future all exist at the same time. What he doesn't know, is if the current timeline can change when something is changed in the past. The US government wants him to find out. The theme being to make right what once went wrong. The time travelers meet all sorts of 20th century characters, but, someone is trying to stop them. Once they return to their present, things may not be what they appear.

2nd edition paperback available on Createspace: https://www.createspace.com/3493536