[gmx-users] Time step in md

[DimitryASuplatov]

Hello,
could you explain my the secret of choosing to time step for md
integrator? I want to perform a 10-20 ns simulation in water in order
to, for ex., calculate some interactions or to see if the structure
would relax to a stable state. 
If I use vsites, heavyh and LINCS I can run with 6 fs step. This would
be quite quick. 
I just wonder if this is `by book`. 
I appreciate your help.
SDA