Here is the full list of all 19 Hidden Through Time achievements. It takes around 4-5 hours to unlock all of the achievements on Windows.
Find All Cavemen Objectives
Find 50 objectives
Find All Objectives of 5 maps
Find 25 objectives
Find 10 objectives
Find all objectives of a map
Find an objective
Find 100 Objectives
Find All Objectives of 10 maps
Find All Objectives of 15 maps
Find All Objectives of all maps
Find All Medieval Objectives
Find All Egyptian Objectives
Find All Western Objectives
Complete an online map
Complete 5 online maps
Complete 10 online maps
Complete 25 online maps
Complete 50 online maps