Albert Barnes Commentary Daniel 1:18

"And at the end of the days which the king had appointed for bringing them in, the prince of the eunuchs brought them in before Nebuchadnezzar." — Daniel 1:18 (ASV)

Now at the end of the days ... - After three years. See (Daniel 1:5).

The prince of the eunuchs brought them in - Daniel, his three friends, and the others who had been selected and trained for the same purpose.