When you submit the registration form, your account is immediately created and an email is instantaneously sent to your email inbox.  You have to click the activation link inside that email in order to be able to sign in on MR and/or to use the lost password retrieval form.  There is no delay: the email is sent immediately when you submit the registration form.  If you attempt to use any of those features before having clicked the activation link in that email, it will say that there is no account with that email or username.

Check your spam/junk folder and look for a recent email on the same date that you registered for a MR account.  If you still cannot find your activation email in the spam/junk folder, then immediately contact your email hosting provider.  You'd be surprised to discover that many cheap web hosting services run by amateurs are not correctly configured and are actually disposing of good emails without even letting you know!  This is a serious issue that should be taken care of, not just because you cannot sign in on here, but also because if they destroy our activation email, there could be many more good emails that you might have lost over the months or years! O.O Note that the issue is on your email provider's side. There is nothing we can do about misconfigured email hosting accounts, as we have absolutely no control over this. Only you and your email hosting provider do, so contact your email provider if this is the source of your issue, not MR admins.