[sqlite] datetime start of day result

[jose isaias cabrera]

Greetings!

if I run this command on the sqlite3 command tool,

select datetime('now','localtime');

I get,

sqlite> select datetime('now','localtime');
2015-07-29 00:48:07

which is correct.  When I run this command,

sqlite> select datetime('now','start of day','localtime');
2015-07-28 20:00:00

I am expecting 2015-07-29 00:00:00.  What does 'start of day' does/means? 
Thanks.

jos?