Disable "of the month" checkbox when send time is cleared
Disable "of the month" checkbox when send time is cleared

When there is no valid send time entered, just as the send button
should be disabled and its message reset to the default, so too should
the "of the month" checkbox and label be reset.

jikamens/send-later,jikamens/send-later,jikamens/send-later,jikamens/send-later