LockClock: Fix lookahead event display

Found out today that events starting at 00:00 the next day were
showing in the calendar when a lookahead time of 'Today' was selected.
The closer the milliseconds were set to 999 (990 for ex.) caused the
widget to attempt to fetch the 00:00 event continuously. A value of
500 provides a safe buffer to prevent continuous event fetching.

Patch 1: Initial patch

Change-Id: I6a0d0795e8970f1491ef198558384db65d639d1e