Picking hello timers for routing can be quite hard - too fast, and you react to short term conditions and flap, too long, and routing is not responsive to improved conditions - a very nice discussion of this is in
talk by folks from the beautifully named startup, "packetdesign".
Floyd and Jacobson discuss the problem of naive periodic timers causing
synchronisation of work in this
paper from a while back
There's a great book about road traffic - see
"Traffic: Why We Drive the Way We Do (and What it Says About Us)" by Tom Vanderbilt;