Is there a way that can I create a recurrence date something like that?
"Last sundays every 6 months @2pm"?
Unfortunately, that's not possible. You can use the "every last Sunday" syntax, but it would repeat each month.
The best workaround in this case would be to set two annual tasks. Assuming you want it to occur on the last Sunday of January and the last Sunday of July, one task could be due "every 24 Jan @ 2pm" and the other "every 23 Jul @ 2pm" as these are the two dates where the last Sunday can occur in this months on the earliest possible date so you won't miss this task.