The mechanism of calculation of additional points differs between original EM and EM engine in RND.
You're right! This was caused by the original code of the native Emerald Mine engine counting time differently than in R'n'D (plus calculating score for all game engines the same way, although it differs between different engines).
Thanks a lot for drawing my attention to this issue!
At first, I thought of full 10 seconds, because DC2 works that way. But I guess I was not right. Believed in RND (Holger

), the first level has bonus score set to 48 points.
You
were right. The "real" time bonus (or exit score) for this level is 30, but was re-calculated to 48 when loading the native level to fit the time score calculation scheme of the original code of the game engine (while R'n'D uses the unmodified time score value).
The guy from YT gets additional 325 points with remaining time about 108 seconds
So, using "30 points for 10 seconds", 325 points for ~108 seconds looks correct (as the original engine code internally does not use seconds, but multiples of eight game frames, which is less than one second, the result can be slightly different than the expected result of 324).
I have fixed this for the next version (patch release), both for native Emerald Mine levels and native Diamond Caves levels, and added a new selectbox to the level editor to show/enter if the time score should be given per seconds left or per 10 seconds left.
An even better sub-second time score calculation (which would be possible using the internal frame counter) is left as an exercise to the programmer...
And there aren't any animations of that calculation as opposed to RND.
Yes, that's right. The original game immediately shows the final score, and then continues counting down the remaining time (including the now meaningless "time out" bells during the last ten seconds), waiting for the player to press the fire button when the level time has reached zero.
Do you think I should add an option to emulate this behaviour?
(This could be a setup option or even a directive for the artwork set config file to force it independently from setup options. But I think a setup option might be the better choice here. The same could be done for a button or key press required to go on after the game was won or lost, maybe. This would also solve the problem of envelope requests immediately after the game covering parts of the visible playfield, which could be seen as undesirable if one prefers to see what's going on on the playfield after the player has won or lost the game...)