Hi,
the worst thing could happen that checkpoint runs immediatly
no problem;
and i am not shure if checkpoint-interval dependes on absolute system-time or is based on relative time-interval ( internal counter )
But this should not be a problem!
think of the switching from winter time to summer time we have in europe. never heared rising problems due to this time-change (1 hour )
Orca

if you have still doubt then
use : ALTER SYSTEM CHECKPOINT;
and switch time after this command
ORca