Clock On Screen is an android app that displays the date, time, battery level and network state as text on the screen.
You can download an .apk file from here. And install it on android devices.
Min API: 15 (4.0.3 ICS) Target API: 29 (10.0 Q)
Check here.
If you got any issue, please report it here.
My native language is korean. So, sorry about that comment in source code is not written in english.
And I developed this to see time at fullscreen easily and to practice coding.