From what little I've been able to glean from the rockwool growers I know, the most important part of cutting down on lag time is getting the block fairly dry before transplanting Into it. The guys in the LP let their blocks sit in a low RH room for several days before transplanting. Some people are even transplanting into completely dry blocks for the first couple days and adding nutrient solution sparingly for the first few feeds.
I did the much more physically ridiculous method of taking the blocks outside and swinging them back and forth really fast to expel as much water as possible. Got them down to easily half the weight of a soaked block. Just like with soil, the roots need to go looking for water in the first week to make a decent root mass. If they sit in a soaked block they have less need to explore and can sit stagnant for a long time.
I also soaked them in a
voodoo juice solution with EC of 0.7 and ph 5.5, so they should have a decent bacterial colony to help them along. This morning everything is perky and looks happy, fingers are firmly crossed.