Striving goals should not have an end date, imho.
(Aside: the current value for ‘no end date’ is the end of unixtime in 2038, which may be nicely correlated with the end of the world as we know it!)
We used to use one-year as the default period for a goal. Seems that it might now be ten years.
Flip side of that default is the fine practice of trying a goal on for size, in which case 30 days is a nice number…