Compare its time in D-76 with another film that you have a DK-50 time for, and give it proportionally the same -- that is, (making up numbers) if Film A needs 5:30 in D-76 stock and 7 minutes in DK-50, and your TMX needs 6:30 in D-76 stock, you'd give it about 8:15 in DK-50. It'll only be a starting point, anyway, and may need some adjustment after you see your results.
That said, Kodak has always recommended avoiding development times shorter than 5 minutes in "small tanks" due to the difficulty of maintaining consistency; that might explain the lack of information. It might also be that DK-50 was an obsolete (as in, no longer sold or supported by Kodak) developer before TMX was introduced...