Twitter does not directly provide the information about when you started following someone. At the time of publication, there are also no third-party applications that will give you the date you started following someone. However, Twitter does list your followers in chronological order. By scanning this list and comparing it to information in your direct messages and Twitter feed, you are often able to estimate when you started following someone with reasonble accuracy. The longer you have been on Twitter, and the more people you follow, the more difficult this process may be.
Log into your Twitter account.
Click on the "Following" link. This will give you a list of everyone you are currently following on Twitter. Notice that your most recent follows are first, proceeding backwards towards the first person you followed on Twitter.
Scroll down the page. As you continue to scroll, more Twitter accounts will be listed. Continue scrolling until you find the person you are looking for. You can also search for the person's user name by pressing "Ctrl-F" on the keyboard and typing the user name into the search field. Based on how far down the name is on the list, and based on how long you have been on Twitter you can estimate approximately how long you have been following this person.
Scan the names you followed before and after this person to see if you can recall when you followed any of them. For example, perhaps you followed a celebrity after seeing a film or television show, or followed an author after purchasing a book.
Check your direct messages to determine when you followed someone, if you followed them recently. Click "Messages." Scroll down the messages for any automated "thanks for following" messages. The date on the message will be the date you started following them.
Scan other messages in your Messages page. Look for anyone you followed before or after the person you are looking for. Use the date on the direct message to estimate the date you are looking for.
Click on the person's profile in the following list. Scan through the person's tweets and check the dates of each tweet. If that person does not tweet often, or if you have not been following the person very long, you should be able to recognise the first tweets you have seen from that person. Look at the date of that tweet to estimate when you started following him.
If you receive e-mail alerts when people follow you on Twitter, and if the person you are following has followed you back, the date of that e-mail will also help you to find out when you started following them.