Yep the fresher dtilt is, the earlier they'll pop up in the air at later percents, and the more likely they'll trip also.
Also... using a fresh dtilt at 50% as an example... you'll get I think a +6 frame advantage or something if they simply get dizzy from the dtilt... this is why the lock is able to work and dsmash because both moves are frame 5 and 4 respectively and are within that frame 6 advantage.
Now if you had used a decayed dtilt at 50%, you might only get a +3 frame advantage instead of the full 6 advantage... which is why sometimes you'll notice that the enemy can throw up a shield when you dtilt and try your next move.
Keeping dtilt as fresh as possible makes the lock and other truer combos much more effective. At the same time, the higher the enemy's health, the more hitstun they'll experience from sourspotted attacks, Zelda's dtilt included... so you ensure a good balance of dtilt decay and the enemy's percentage to take full advantage of dtilt.
It makes a huge difference. It's a fantastic damage racker from simply a frame 5 attack. If you're wise, you can be doing at least 18% damage from every dtilt, combining many different moves. Also... around 70% onwards, if you're dtilt is fresh and you buffer well, you can now start grabbing people as a true combo.
Hope that makes sense!
EDIT::: Also don't be reliant on dtilt early in the match. Always begin throwing it out in your game after 50% so that it will ever really decay too much. Try to rack up damage wisely without using dtilt up to this point with other moves like jab > grab/dash attack, grabs, din's/nayru's as punishers, and various other moves. Just play safe up to this point and then go aggressive with dtilt after this percentage but don't use the lock, end the first dtilt with a move of your choice here:
http://www.smashboards.com/showthread.php?t=218082