It takes at least two weeks for Java fern to attach properly. With that said, every Java fern is different. In some cases, it can take up to six months for a Java fern to properly attach.
How long this process takes depends on its growth rate and the type of surface it’s trying to adhere to.
If you want to make your Java fern attach faster, try affixing it to a rough surface using a cable tie. Generally, the rougher the surface, the easier it is for the fern to attach.
Furthermore, you can increase the plant’s growth rate by using fertilizer, exposing it to 8-10 hours of light each day, and cleaning the tank regularly.