Can i just put the 3' feet cutting in a gallon
of water?
Will it take a little longer to root?
How often do i need to replace the water?

Ive' rooted quite a few cuttings in water, it is pretty effective, but also some what controversial. Roots formed in water are different than those formed in soil and the cutting has to adapt from water to soil. Another thing I have done successfully is to put them in water for a few weeks then move to moss.

I've seen cuttings being rooted in water, but I've never tried it. I think the moss method or Jon's paper towel in a bag method are faster ways of rooting cuttings. But its always nice to experiment, that's how we learn. Here are a few videos of a fellow rooting in pure water.

Yes when you see that white stuff a week or so after I put some in moss and left some in water, the ones in moss then did seem to root faster. And yes every 3rd day or so I change the water too. Oh I forgot to mention, I generally only use an inch or so of water, but with a long cutting like that, maybe a bit more is in order. I have had great success with that method.

or stick it in dirt... Perlite and potting soil. Lately orchid mix has done well for me

good luck

some people root in water without an issue. i tried it and none of them took. i might be doing something wrong. my mother roots in water all the time with number of different house plants. whatever works, stick with it. i like paper towel and baggie.