Here is a sample solution of the CMakeLists.txt for the time travel interface library.
# [project]/time_travel_interface/CMakeLists.txt
add_library(time_travel INTERFACE)
add_library(time_machine::time_travel ALIAS time_travel)
target_include_directories(time_travel INTERFACE include)
Project settings
Interface libraries can also be used to define project settings.
For example the required C++ standard or additional compiler flags.
Attention: Only define compiler flags if you have a really good reason.
Adding compiler flags will break the portability and compatibility of your project.