This is one of the first apps I got when I bought my first iPhone (the 3GS). I still use it every single day. It’s my bedside clock on my iPad. When I play a gig, it is running on my iPhone on my music stand so I can keep track of the time. And I use it every year on Dec 31 because it gives a ten second countdown to midnight then shows fireworks.
SSteve about Atomic Clock (Gorgy Timing), v4.50