Aloha I_AM_Healthy,
Generally Chunyi talks about spending 75% of your practice with active exercises and 25% with the sitting meditation in the beginning as you are taking care of physical issues.
I can't speak to the length of your personal inhale length, but the breath is to be relaxed and and even, not forced or over-worked.
Some students have a favorite "made up" meditation that works for them. Does yours work for you? I have been doing a water meditation, but there are things with that that I need to keep in mind as well, such as not doing deep meditation in cool water.
Much Love,
Shawn
