Hello.
How can I restore my Linux setting after a specific time? For example, You want configure SSH on a remote web server but if you did a wrong command and your connection to a remote server lost, After a specific time the SSH configuration restore to default.
How can I do it?

Thank you.

Not really following you on this in regards to "SSH configuration restore to default", however I do have a suggestion.

If you are going to run things on SSH and fear you may lose connection then use 'screen' or 'tmux'. If you lose connectivity then you can connect back into the screen or tmux session afterwards and carry on from where you were.

No undo, no reset. This isn't a video game.
You messed up by not verifying from a secondary terminal that you could reconnect.

Experience. Priceless. and Funny.

If we are talking about resetting the system, then there is such an option. Snapshotting, of course it'll reset EVERYTHING!. Some filing systems support it, as does LVM. Also if it is a Virtual Server then the hypervisor may also support doing it. Heh. But again it resets everything . Oh and of course, too late to reset if you didn't set-up the snapshot prior to the event!

You can make a second server configuration file (sshd_config) and launch a second instance of sshd. Use the -p option to force it to use an alternate port. Then you can test it with the alternate port.

With that you can connect once to the server on port 2345 and the logs from that session will be in a separate file. When the session is over, sshd ends. The whole time, the original server never goes away.

Otherwise, you can make a backup copy of the file and then use an at job to restore from the backup copy and then restart sshd

If my server is in another country and did a wrong command and blocking myself then how can I solve it?

There will usually be some kind of console access at the hosting provider which you can use to interface with the lost system.

Usually prevention is the best policy and if you are messing with iptables you can use iptables-apply or at to help out. The latter can be set to restore the last known good configuration after a timeout. It can also be used for messing with sshd configurations though when testing that, it is best to leave the existing SSH server alone and start up an alternate SSH server on a separate port using the -p option with the second instance of sshd.