if your going with rockwoll, ive always soaked my cubes for a few hours with the water phed at 5.5 5.6, and with the paper towel method you have to get the seed out pretty much when you start to see the tap root come out as chigga said the roots have hairs that will get entangled in it and rip partially, and kill or stunt it, if your doin the sol cup wich i also do i use fox farm light warrior for starting seeds, make a few holes at bottom fill with te soil and just plant the seed, best way to go like he said, basically skip the paper towle method if you keep have 1-6 2-6 pop eveyrtime. like you said no point in wasting seed.
and with the soaking usaully its for older seed due to the lack of moisture in them, the longer they take to sink is a good indicator of how old the seed is, but i have sucess with seeds that take usaully 24 hpurs to sink then plan it in the fflw and they sprouted with in 36 hours and so far out of the seeds i have started i only lost aboout 1or 2 out of about id say a good 25 30 seeds and i think both times were with the paper towel method with leaving the tap root get to long in the paper towel.
hope this helps. as these are just some of the ways i have had sucess