The exclusivity period should be 8-12 weeks normally, on the basis a deal has been agreed in principle.
Here, it seems it would last as long as Textor needs to sell his Palace shares.
Surely he anticipates selling them within the same period as it would take to conduct due diligence.
If he has gone into an exclusivity process with Moshiri without being fairly sure of the timescale of the disposal of his Palace holding, then he isn't serious about buying Everton and is treating the club with a certain disdain.
I do not see why he could not have waited until his Palace stake was sold. In the aftermath of TFG, there is not a queue of buyers so what difference would a few weeks have made?