I am not sure how long the air out time would be but I would be nervous about having a gecko be in a terrarium where it can lick the wood that was stained. So after airing it out for the stain, maybe put clear acrylic or glass between the wood and the inside of the vivarium. This way you can still see the wood stain color but the gecko can't lick it. You could also look up some sort of clear non toxic varnish to paint over the wood, then you don't need to use glass or acrylic. Clear Varnish - Organic Eco friendly VOC free Odor free - Other Wood Products - Clear Varnish - Clear Varnish (1 Quart) - Organic Paint, Odorless, 100% solvent and VOC free, non-allergenic superior quality paints from ecos and varnishes
This is a type of clear varnish for wood that states it is safe for animals and children.
Also certain types of wood can be poisonous or release fumes too.
Have you already stained the vivarium? That website also has safe nontoxic stains.
I have already stained it but planned on clear coating it was just worried about fumes getting to the leo's. Thanks for the link I am going to see if some of the home improvement places around here might have something similar since I would need to clear coat it. I just hope I can find a clear coat that is VOC free.