Maybe a bit to late for an answer for you but maybe someone else has the same question (like me). So bumping this old thread is intentional as it is one of the first result from google.
That said, here is the solution:
Just put the node 'text input' (from plugin https://flows.nodered.org/node/node-red-dashboard) in your flow, double click it and set 'mode' to 'time picker'. Thats it!
But be warned: This input is rendered as HTML tag with type=time and every browser renders it differently. In Firefox you have to use the keyboard as to type times, in Chrome you also have small up/down buttons and Microsoft Edge provides a nice, touch friendly picker.
