Conversion time/speed is not a problem but I do feel safer if it took
a tad bit longer than XnConvert which converted 407 BMPs to PNG, 0
compression in 39 seconds. I’m not sure if that’s normal.
You shouldn’t be that concerned about speed in a conversion process like this since BMP and PNG are lossless image formats, but PNG is lossless and compressed. Meaning you should not experience any quality loss at all as your conversion program simply shuffles the bits from BMP to PNG format.
As explained on Wikipedia, this is what BMP is all about; bold emphasis is mine:
Typically, BMP files are uncompressed, and therefore large and
lossless; their advantage is their simple structure and wide
acceptance in Windows programs.
And here is what PNGs are all about from that same article; again bold emphasis is mine:
Compared to JPEG, PNG excels when the image has large, uniformly
colored areas. Even for photographs – where JPEG is often the choice
for final distribution since its compression technique typically
yields smaller file sizes – PNG is still well-suited to storing
images during the editing process because of its lossless
So depending on your computer’s speed and power—as well as the size of the images being handle—being “slow” when converting from BMP to PNG is really a non-factor. Both are lossless formats with the main difference being that PNG compresses the data while BMP is basically raw and uncompressed data.