paulrosso,
It's only possible to sort in alphabetical order, priority order, or by due date.

I think these three options are not enough.
Is it difficult to add some more options
including created date time of tasks ?

I agree with tsasaki. The ability to arrange tasks in any order should not be hard as this is standard functionality. Virtually all iPhone apps that are centered around lists have this and many list websites also have this.

while I also have found myself wishing for sort by task creation date, as someone with some experience in the world of high-volume databases, it is not a trivial thing on many database platforms to just throw in a new way to sort. This would involve writing new indexes for the back end database. In some environments more indexes can slow things down under some circumstances, or can tax storage capacity.