In the new Launch Lightning SFM Delivery, you cannot select part of the time stamp in date/time fields and type what the new value should be. You have to remove the entire time value and type it in one go from start to end. This is very impractical. It should be possible to change 1 of the digits or all digits you have partially selected.
to change the start & end minutes from 5.00 to 5.15 you have to highlight the first 0 then type in 1, then highlight the second 0, and type in 5. You cant just highlight or backspace over them any more
What is the underlying problem do you intend to solve with this idea?
Make it easy to modify values in date/time fields
How is the problem being addressed today, if at all?