Using the Twitch Tools Following Length tracker you can figure out how long you have been following a specific Twitch channel. This is a fast, easy way without having to generate a full CSV spreadsheet.
We also run a more sophisticated tool to track Twitch followers. That version helps you generate a spreadsheet of all of the followers of a channel or all of the users that a specific channel follows. It includes the date that the user started following a channel, if they should be alerted when they are streaming and more information.
Put your Twitch user name and then the channel in the boxes below, click Fetch results and you're in business.