A sign-in lasts at most 24 hours. While a console tab is open and you've used it in the last half hour, the session is renewed in the background, so a working day rarely reaches the limit.
When it does end, the console shows a signed-out bar and the page you were on keeps what you typed. Sign in again from the bar — it opens in a new tab — then come back to the original tab and carry on. Nothing is submitted while you're signed out, so a form that failed with "unauthenticated" was not saved or sent.
Ready to see it in your own console?
Posting and reviewing are free. Every stage, e-mail and export described here is in the console from the first sign-in.