What Michael says is my experience too. But remember, you must have a minimum of time to acheive thorough saturation and then even development.
I never dev a print for less than 2 min, usually LPD 1:2. I would use 1:1 only if I wanted a denser black and experienced fog with longer time. (To me this would be a very thin negative).
However, I generally use contrast adjustment to alter "blackness" in the shadows (I use Ilford MG Warmtone), and keep development time a constant. For acheiving different "tonal" qualities, you might try different paper/toner combinations, rather than varying development degree (either by dilution or time).
Ansel A once said that as developer becomes weaker (or if more dilute from the start), increasing time will yield the same results (up to when chemical fogging might occur). I never tested this.