get hr from time stamp in a text file

how to get just hours from time stamp hr:min:sec from a text file.

There are varible logs entries (ex: 1st has 3 , 2n has 10 etc )to each hr in the log text file. I should be able to pic hourly entries for each hr on a given day and perform some logic and display it to another text file. 

any help on this would be appriciated