From the point of view of Q++Studio, a grid is splittable if it has a high enough symmetry and Q++Studio can figure out unambiguously which dates belong to which pages.
This means that a splittable grid must:
•either have an even number of pages, and a number of periods (days, weeks, months) which is divisible by the number of pages.
•or use DayValue Marker tokens to specify which dates belong to which page, unambiguously.
If the option to start on the left or the right is disabled, even though the current grid should be splittable according to the above guidelines, then make sure that the current grid's template was not scanned with the option Do not split set to true.
Note that sometimes Q++Studio will split a grid automatically based on the structure. For example if you have a 7d/2p grid with Mon-Tu-Wed on the left page, asking Q++Studio to start on a Thursday will cause it to start on the right page.
See also: Making Splittable GridTemplates.