Change input from analog to digital clock in Google apps
Sadly, it's not possible to use a keyboard with this new type of time picker, because it is not a feature of this mode ("clock", right image) of the control. But if the developer of an app showing the time picker uses the classic mode ("spinner", left image) which is still present in newer APIs (21+), you can use the keyboard. 

Maybe if you give feedback about this annoyance to Google, they will enable the use of keyboard as an alternative to manually selecting the numbers in the radial clock for newer versions of Android.