I concur with HerrBag and Ken.
Flexibond is an excellent product but it was overkill for this installation. It’s a modified thinset basically to give some flexibility when installing over an existing floor e.g. vinyl or wood where there may be a slight “flex” in the underlying floor.
Why do you think the mortar is still curing? Do you mean the grout is still curing? It shouldn’t take more than 72 hours tops, even with all the polymers in the mortar. Did you add Admix to the grout as well? That would increase cure time.
Your concrete substrate is great unless it’s smooth as Ken mentioned. What’s done is done. From here I would let it cure fully 72 hours before the heavy laundry machines.
Additionally, I think it would be wise to set the machines on exterior grade 3/4” plywood. You could use one sheet for both machines or cut to dimensions at the base of each machines + 1/2” on each side for a less detectable finish.
Reasoning here is that because of all the mentioned factors re: tile material, modified mortar, possibly smooth substrate, the fairly intense and constant vibration of the machines could, over time, loosen the mortar/tile bond and dislodge or break the tile. Stabilizing the machine on the plywood would reduce the stress on the bond.