Yea the default (Creality) firmware has a lot of quirks, doesn't save settings to the board (saves it to the sdcard), doesn't show long filenames or much info on the print screen, etc.
The new version (from a second developer) is up since 3 days ago, but only in an uncompiled format. Hopefully they have pre compiled versions posted soon
Calculating completion time is not an exact science, either. It likely averages the future layers on the past time, based on # of layers left. But sometimes the higher layers may have less material to print, so it may take less time.
The time estimated by Cura (or the slicer of choice) is what I usually go by, and it is usually fairly close.