You don't have to use a timer, you can also do it when you're about to use the token, or after the token has been rejected if you're so inclined. I.e. before yo

You don't have to use a timer, you can also do it when you're about to use the token, or after the token has been rejected if you're so inclined. I.e. before you make a request you check the validity of the token and if it's not valid you refresh it; or if you don't do this validation you'd have to deal with the server rejecting your token, doing the refresh, and then trying the original request again.