Hi, I received a prayer plant cutting that is currently still in water and the roots are about 3" long. I'm a bit nervous about transplanting it into soil, and was wondering how long the plant can stay in water? I feed it liquid plant food (very diluted because i'm scared of burning the plant) every time i change out the water (1x a week).

Wait for the roots to get about six inches long. Get a 4" plastic pot, fill it with good quality potting soil up to the brim. Water the soil well. Soil will "settle" after watering.
Plant your cutting the next day. With your index finger or a pencil, make a hole in the center of the soil, an inch round and two inches deep. Take the cutting, place the roots all down into the hole, gently tap in soil around the base of the plant. Guaranteed easy, guaranteed to work for you!

BigBill said:Wait for the roots to get about six inches long. Get a 4" plastic pot, fill it with good quality potting soil up to the brim. Water the soil well. Soil will "settle" after watering.
Plant your cutting the next day. With your index finger or a pencil, make a hole in the center of the soil, an inch round and two inches deep. Take the cutting, place the roots all down into the hole, gently tap in soil around the base of the plant. Guaranteed easy, guaranteed to work for you!

Thank you! Will try this out! Does the method also work in general for other plant cuttings rooting in water?

I have done cuttings this way many times, begonias, African violets, Swedish ivy and more.
With larger plants I fill the new pot 2/3 of the way with soil, water then create the depression in the soil, place the plant and gently back fill with soil.
I plant just about everything in soil by this method. Dahlias too.

I would also add perlite to the soil , I do a 50/50 mix

Never been a big fan of perlite. Generally I have found perlite to be too small in particle size.
In my orchid mix, I use "sponge rock" in a medium grade. Particle size is up to a half inch. It is like perlites' big brother. I find by adding some to potting soil, about 10-20% by volume it absorbs water like its little brother perlite, but due to the particle size the mix doesn't get too dense. It stays more open and airy but yet still holds more water if it wasn't added.
Just a suggestion.

Orchids and other epiphytes do require a much airer potting mix than terrestrials. Thus, it does make sense to use a potting mix with particles that are larger than perlite. However, I do think that perlite is a better choice for non-epiphytes. Of course, it also depends on your watering tendencies.