If you want to display the time directly on your wallpaper rather than just in the top panel, extensions are the best solution. Timer/stopwatch in Ubuntu 14.04 Unity?
Dedicated applications provide tools for time management that go beyond just showing the current time. GNOME Clocks download clock on ubuntu
A fully-featured alarm clock that lives in your notification area. It supports repeatable alarms, snoozing, and flexible notifications like playing music or launching apps. Use the official PPA for installation: sudo add-apt-repository ppa:tatokis/alarm-clock-applet . Desktop Clock Widgets and Extensions If you want to display the time directly
The standard clock app for the GNOME desktop, featuring world clocks, alarms, a stopwatch, and a timer. It is lightweight and integrates seamlessly with Ubuntu's notification system. Install it via the Snap Store or using sudo apt install gnome-clocks . GNOME Clocks A fully-featured alarm clock that lives
Originally designed for Plasma Mobile, this is a highly capable clock app for desktop users wanting a modern interface for multiple alarms and timers. It is available as a Snap package . Alarm Clock Applet