Hey there! On Java Moss... it actually takes a few weeks to attach. You'll want to check it when you think you want to take off the bands and gently tug on it to see if it's growing onto the rock (or whatever you attached it to). Might take longer, might take less time. With Java Moss you really want to make sure it's got a good firm grip before letting it go on its own, elsewise you'll have bits drifting off and getting unattached, or the bits that aren't attached drifting off and pulling the attached bits with it. Really a pain. But once it's stuck, you're good!

The fern usually grabs easier, I would think in a few weeks it should be good. Cheers!