Sometimes, ISPs (internet service providers) throttle your connection to out-lying servers. It might be the case that during peak times, your Internet provider might be throttling connections, I know that they do this in European countries, however, in the USA, I'm not too sure.
Also, as suggested above and on previous comments, it (the lag) might be because of poor connection between you and your router and perhaps too little bandwidth to support the ever-increasing usage of Internet capable technology in the 21st Century.
I would suggest either of the two, calling up your Internet provider to address the issue to them, buy an Internet plan which provides you more bandwidth (upload and download speed), purchasing a better router or directly connecting your computer to your router through a LAN cable as Wi-Fi is generally less reliable in terms of connection stability.
Hope to have helped.