Night viewing at Nijo Castle

I've seen a few references to Nijo castle being lit up in the evenings during Sakura with special late opening.

Do you know if it is possible to see all the castle and gardens at that time, the same as during the day or is it limited access for cherry blossom viewing and would we be better to go seperately in the day to see the palace itself? I presume they are seperate access tickets and you can't just go late afternoon and do both?

Do you know if it is possible to see all the castle and gardens at that time

No, it is not possible. Most importantly, the Ninomaru Palace (the castle's main attraction) will not be open.

I presume they are seperate access tickets and you can't just go late afternoon and do both?

Your presumption is correct.

Here is the official pamphlet in Japanese:
http://www.city.kyoto.lg.jp/bunshi/page/0000111641.html