Tannins in my fish tank?

the driftwood will not change the pH in any significant way to affect fish ... and unless you are using an established filter, you will be ready for fish in 4 to 6 weeks ... if the pet store told you 24 hours, they lied and if you stock your tank with fish, they will die ... the tank needs to be cycled first ... and that takes 4 to 6 weeks not 24 hours ...