How to print the merged column in the beginning of the merged region to print in the beginning of the subsequent page when the merged region extends beyond single page?
If the rows-per-page is consistent and predictable, you can pass an appropriate key to the merge() function to prevent merged regions from spanning pages.
For example, in your report there are 85 rows per page, use a cell function like:
#write(DaypartDisplayName) merge(DaypartDisplayName & trunc((row() - 1) / 85))
Be careful to keep row heights consistent as messing with fonts can modify it and give you inconsistent results. Also please note that, if the font metrics is different on the users system then the number of rows may change causing unpredictable results.