Depends on your company procedures again. We set 3 times 1500 for normal climbout procedures and SOP says VNAV on at 1500. We had our SOPs allready changed for 10.8 (VNAV/LNAV selected at the gate), however boeing really did a blunder with that version. Had to change all aircraft back to 10.7 pretty soon after they introduced the bugged version.
If you select VNAV before the selected climb thrust reduction altitude nothing will happen until that altitude, and then you will get a normal climb thrust reduction and speed cursor moving up.