assalamualikum. Well without a doubt mehdi and isa (pbuh) will return before the end time, and this is documented well. The question of 'when' is unknown. There are several reasons for that. one of them being that it's in the domain of AL-Ghaib (unseen, only allah knows). The other reason perhaps being is we cannot predict very well the length of miner/major signs. A sign could last for a few decades or on the other hand just for a few weeks. Only allah possesses the knowledge of the length of each individual signs.
I had one question for the brothers and sisters on tti. We are told that minor signs are almost over, then again we are told that minor signs can repeat themselves. What if many of the minor signs are yet to repeat again? if that's the case, then it could perhaps be a long time till the major signs take place. I am not predicting anything, im just curious.