Timer relay with three buttons

if you know any project with same target I would be glad to have a link!

Very unlikely.

Have you looked at the examples in the IDE ? They will show you how to read a button, set the state of an output and deal with timing.

NOTE : because of the requirement for an emergency stop button you will need to use millis() for timing and not delay() so it would be a good idea to read Using millis() for timing. A beginners guide and try the examples that it comtains