.csv file of every block timestamp in btc history
You can use https://blockchair.com/bitcoin/blocks.
It is limited to 1 million cells for free, but as you only need "Time" and "Height", just:


deselect all checkboxes but "Height", and click on "Export" selecting then "csv". Open this file with your spreadsheet app.
deselect "Height" and select only "Time". Export. 
Open the file from (2), copy the column, and paste it next to the first column in file from (1).
as the results are both ordered by time, rows coincide and you already have the desired data!