My mother bought me one of those Estaban guitars for Christmas and I am sitting here working my butt off to tune this thing. This is my first experience with nylon strings but I am wondering if these things need way more time to stretch than steel strings. Does anyone have any experience with these flamenco guitars that knows anything about this?
Thanks in advance.

Yes, nylon strings take a while to hold tension. Next time, it is a good idea to just hang out with your strings and stretch them out one at a time, putting each back in it's little paper envelop before taking out the next one. I've never "over stretched" a string during these pre-stretches. Also, after you tie the knot at the bridge (I'm assuming your tying knots otherwise you're using ball end strings) place a thumb on the knot (if you're paranoid like me) and stretch the string out with the other hand before sending it through you're tunning machines. "Boing-boing-boing" it for a while and hold it stretched out, this will go a ways towards getting it stable.

Then what I do is tune it up a half-step sharp and let it sit till the next day. It will usually hold it's tuning good enough to practice. I've never performed on strings that were less than one week old, but never older that three weeks old (that latter part just sort of works out that way, but I was always a stickler for chaning nylon string a week before a performance back in college when the nylon string guitar was my primary weapon).

While I'm at it I really like D'Addario Pro-Arte strings: the "normal tension strings" for the their sound, and the higher tension seemed to last longer.

Wash you're hands and dry them like an obsessive compulsive and they'll last a bit longer too (at least the voices in my head tell me so).

Merry Christmas