Okay so take this with a grain of salt, cause my cloning experience is with a completely different plant.
Using a rooting hormone, I have usually had roots form within 2 weeks. So long as the stem and leaves are looking fairly healthy though do not worry. So long as proper moisture levels (like 90ish% rH levels) are maintained the cutting will eventually grow roots.
I would use the cuttings in the fiber pots and water as your marker, pretty soon you should see roots poking through the pots. If no roots are showing and the sprig is still being a trooper let it sit. If you start noticing the base of the stem starting to look weak it is probably giving into infection and should be removed.
Feel free to ask any questions
Some of my recent reading of hop growing has confirmed my belief that they are a typical vine, in that if not kept in check they can easily become invasive. Vines have multiple ways of reproducing, unlike for instance most trees. They put out these vines, the vines touch ground and put out a new set of roots, potentially 20 feet away and thus colonize an area. A great example of this is in the typical 'strawberry pot' where they have a main top area for the initial planting and then mini areas for vines to essentially clone themselves.