"the delay usually refers to the fact that you have to move your feet from "heels on the floor" to a position on the pedals where you can apply brakes"
Well, thanks. I didn't really thought about that!
"also, if you apply manual braking immediately on touchdown it may cause the Nose gear to slam onto the runway"
I guess this will not happens as long as I apply manual brakes 'smoothly' and 'constant' as the FCTM said. Unless the antiskid in inoperative:
"When the antiskid system is inoperative, the following techniques apply:
- ensure that the nose wheels are on the ground and the speedbrakes are extended before applying the brakes.
- initiate wheel braking using very light pedal pressure and increase pressure as ground speed decreases
- apply steady pressure and DO NOT PUMP the pedal"