Send/forward email to firstname.lastname@example.org or email@example.com or <whatever time length>@followupthen.com and it will be sent back to you in that time. Try sending an email to firstname.lastname@example.org to try it. No need to create an account.
I love this service – I can forward emails to email@example.com (or whatever time) and delete/file the email to get it out of my inbox. It’s one of my current favorite finds.
There’s no account creation (unless you want to for advanced features).