Kid Learning Chess - When to Introduce Clock?

Hello,

  First time poster here.  My 9-year-old son has been learning chess and getting quite into it.  He's primarily been using Chesskid.com, and is well past how pieces move, using pieces together, and basic checkmates.  He seems to be grasping more complex tactics - to be honest, I'm catching up on my parent account on Chesskid, just to see what he's learning.  I introduced notation to him, and when we play together now, I have him writing down our moves (something he's taken easily to.)

I thought maybe it was time to introduce a clock with a generous time on it (for us, 25 mins each seems plenty).  I'm looking to get an opinion here.  Is it an appropriate time to introduce the clock? I'm concerned that the presence of the clock is making him rush (he finished our last game with 13 minutes still on it.)  The upside is getting him used to the clock, and also to have it as a tool to understand that he DOES have plenty of time to think.

Thoughts?  Thanks!

P.S. I'm essentially a beginner myself - I've played on and off for years, but this is my first concerted effort to start playing better.  Currently rated about 1100 in correspondence chess on Chess.com.

My opinion is the sooner, the better.