MariaDB: Querying a timestamp partition
Your expression is too complex.  There are many severe limitations of what can go into BY RANGE.  Use simply UNIX_TIMESTAMP(time).  Even if it would work, FLOOR does not add anything to the expression.

BTW, the trailing hh:mm:ss is optional in this situation.  These are identical:

UNIX_TIMESTAMP('2015-08-01 00:00:00')
UNIX_TIMESTAMP('2015-08-01')


Now, on to my favorite question:  Why are you using PARTITIONing?  PARTITIONingdoes not inherently provide any performance.  There are only a few use cases I know of where you can trick PARTITION into providing more performance than a carefully chosen index.