How long after drinking alcohol do I have to wait to take. 25 mg xanax (alprazolam)? I do not take Xanax (alprazolam) regularly, I only use it situationally.

Until you are sober. I would not recommend taking xanax (alprazolam) at all, until you're completely sober and you have been prescribed this by your physician. If you're being treated for anxiety or depression, i would suggest stopping alcohol because it complicates your recovery. If you're withdrawing from alcohol and having anxiety & shakiness related to that, i would suggest getting help for your alcohol abuse.
Be careful. Theres no specific time or alcohol level i could quote as alcohol reacts differently with everyone. Alprazolam and alcohol share some of the same receptors. This means thexanax could significantly potentate the alcohol. Caution!