Salaam Respected brother, Permit me to say this - I think both approaches are incorrect. There is nothing to indicate that the mahdi will appear within 20 years and there is nothing to say otherwise. This is from the 'ilm ul ghayb. The best we can say is Allahu a'lam. I am just a bit perplexed as to how the thread shifted to Shaykh ul Islam ibn Taymiyah?!