Mysql Alter Tables took 5 hours to add 1 column
In my experience with MySQL Cluster, I found pt-online-schema-change as a very handy tool for appling live schema changes.

It works this way:


it creates a new real table B (with temporary purposes) as clone 
of the table A that you want to change
then applies the schema change to table B. The operation is fast cause the table is empty and has no traffic on it.
it creates a trigger so that new records inserted in table A will be copied into table B
then slowly copies records from A to B in small chunks of data
them with atomic RENAME TABLE operations B becomes A


I'm not sure if it works with all kind of schema changes.

If the table is big, it will take a long time, but the table will remain available for read/write queries.

The mysql user that runs pt-online-schema-change must have particular privileges, but this is not clearly explained in the documentation (I've opened a bug ticket about this)