How do I calculate how much time has passed since the most recent block (via blockchain.info's api)?

I have managed to get a the websocket connection working, and am receiving data from ping_block and blocks_sub. However, I am having difficulty doing the math between the current date and block date received from blockchain.info's api. Can anyone help with the code for calculating how much time has elapsed since the most recent block?

Any advice would be appreciated. Thanks.