I was also told, that its not exactly a catalyst, as in, after the 48 hour pot life, the product is still perfectly usable, but the crosslinker is no longer active after that time, but you can simply add more, so thats pretty cool.
Old masters hardener is not listed what the mechanism for cross linking is but TBH it sounds similar to aziridine cross linkers like Dalys and more than likely that is what it is. 48 hours life, then add more if need. aziridine based crosslinkers are unique in that they can be added to pretty much any acrylic finish.
Dalys crosslinker is 73% propylene glycol / 27% aziridine.
Lenmar crosslinker is 100% aziridine.
Interestingly the Daly's crosslinker would probably work nicely as both a crosslinker AND a latex extender like XIM due to the high amount of propylene glycol.