I don't know about the sync time, but delay time is how long it takes the mechs to respond to your controls.
the lower the delay time, the faster the mechs respond to your keypush.
At high delay times, the mechs move like half a second after you push the buttons, but the graphics will be much smoother.
But at low delay time, the graphics could skip a lot.
It's really a tradeoff.
YSK (the producer) recommends delay time of around 5 on low pings, and 10+ on higher pings.