crontab syntax

[mahesh]

running 21.10

i want this script to run every 4 hours starting at 00.30

30 00,04,08.12.16.20 * * * xmessage -display :0.0 "one bell!!!"

is the above correct or is there a better syntax to use
/tks
quote:He that would live in peace & at ease, Must not speak all he knows,nor judge all he sees.'