If they were to confront one another, in a timeline wherein their world's still exist as separate and distinct after the Crisis on Infinite Earths, how would these counterparts stack up if pitted against one another. Both were genius-level scientists, with Danton Black turning towards costumed criminality while Rex Tyler became a costumed crusader for justice. Each has the strength of multiple men, with various minature versions of themselves which they employee on their adventures, and wicked fashion sense. Considering Danton as Multiplex has nuclear powered might while Tyler as Hourman gained his ability on a chemical Miraclo pill, it would seem that the radioactivity that Danton would emit would irradiate and thus eliminate the effectiveness of Tyler's pill.
In fact, the opposite would probably be true, as Hourman's abilities caused him to act in a hightened and irritable state when his new and improved Miraclo was used during the silver age when exposed to the atomic-like bioproduct emitted from his partner Doctor Fate's own energies. Hence, there would be a significant power boost which would help Tyler match Multiplex's seemingly superior superstrength, much as it had with Doctor Fate's own unearthly might. And given his significantly lengthier career, Hourman would best Multiplex in battle given his extensive training. However, the mini-Multiplex's may well overwhelm Hourman's Minute Men, who themselves gain only short lived powers compared to the Man of the Hour's sidekicks. Still, considering that the clones are dependent on the mental state of their master, these Multiplexes could well be vanquished by the Minute Men if Tyler defeats Danton quickly. Which, we surmise, is what would occur.