In case anyone is interested. I found this chart of travel times to be useful as I planned and tweaked my map. Travel times were taken from spawn to obj at a run, but no sprint and no strafe jumping. Actual travel times would depend on your jumping ability, the relative amount of downhill, and stamina.
http://www.planetwolfenstein.com/4newbies/et_differentials.mht
Naturally, if attackers’ travel time - defenders travel time > spawn differential, then the obj is defensively biased.