The bottle on my counter says only 3 days, but I've used it to about 5 if I don't contaminate the food by spooning it out, but pouring it instead. Also depends on the amount of preservatives in the food, FYI we use organics with only vit C added.
First off, check out the subforum dedicated to cresteds, you'll find almost any question there you could think to ask probably already answered.
But in the meantime, you should really think about crested gecko diet (CGD) by T- Rex. The majority of owners swear by it. It is a complete food, all the vitamins, minerals, protein, fat, and fiber your little guy/gal needs. IMHO, the best way to raise a crested is offering CGD (mixed with babyfood initially if they don't partake of the straight diet.) and crickets for extra growth punch. After they reach adult, you can feed only CGD, but we still treat her to a few crickets every week. (Which is probably why she's a bit on the chubby side, but we're trying to fix that too.) I like CGD because it lasts 6 months open on the counter, you just mix with water each serving. I also don't like worrying about her calcium intake, whether the crickets undusted themselves before she caught them for instance.
Welcome to the world of cresteds! Good luck with your little one!
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0.1 Albino Leo Gecko
0.1 Crested Gecko
1.0 Dear Boyfriend
Departed: Harvey and Spock