Some people do it right away - some wait until they think it's dirty enough to clean it - some never completely disassemble their Glocks... So how long did it take you to fully disassemble your first Glock?
First one was a couple of weeks before I started trying to improve the trigger pull (long line of 1911's). Every one after that was run 200 rounds through it to wear off the copper paste then completely tear it down and start polishing.
Bought a G17 from a pawn shop (killer price) and took it home. It was torn all the way down within 10 minutes. Replaced all the springs, firing pin and guide rod. (I had the parts sitting around and could not resist)
I always clean all of my firearms prior to shooting for the first time. Not a full strip but I'll clean the barrel and place a VERY small ammount of grease on all friction points prior to firing. If I shoot lead in the gun I'll clean about every 500 rounds, if I shoot jacketed only it's when I feel it needs it, could be a few thousand depending on the volume of powder residue I see.
My Glock for a complete detail strip ? 9 years for my first one which was a new 27, 1 week for my G21 and G22 which were bought as used trade in's. Glad I stripped my G21 since it looked new out of box till' I started pulling stuff apart, a lot of sticky crud all surfaces that were not visible. Looked like it was dropped in a tub of corn syrup for a day then pressure washed and the safety plunger was really nicked all up along the center rim/catch.
When I bought my first Glock it was a duty weapon. I really wasn't too familiar with them and it was a couple of years before I detailed it. Then it was only after buying a video that showed me how to do it.
It was a couple of weeks. I used to own a Ruger MKII Stainless government slab side pistol. Great .22, I could hit a nickel every time at 25 yards. I had it completely apart a couple of times, and it is a really difficult gun. My G17 is really really easy. I used a video on youtube to take it apart, but once it was apart, I decided that I really didn't need the video, because it is such a simple mechanism.
I purchased my first GLOCK in Jan 1998. Between Jan 1998 and Oct 2009 I never once detailed any of the dozens and dozens of GLOCKs I owned. In Oct 2009 I attended the GLOCK Armorer Course and realized how easy it is. I do it all the time now.
In fact, I taught my 6yo daughter to do it. She can't physically manipulate it due to lack of strength and small hands but she can walk me through dissassembly and reassembly. We do it now as a party trick. The wife just rolls her eyes.