Menu libaries for a clock
I would make it myself.

One way to do it:


Create an enum with all states, like Normal, ChangeMonth, ChangeDay, ChangeHour, ChangeMinute };
Use one button to increase the item you are changing with 1
Use the other button go to go the next enum


You can make it fancier by using longer/shorter presses (e.g. to increase faster)

Don't forget to debounce button inputs.