Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Make a new theme with a file called Info.plist that contains the following (enable in Winterboard):

Code:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>TimeStyle</key>
	<string>display:none</string>
</dict>
</plist>

Code:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>TimeStyle</key>
	<string>visibility:hidden</string>
</dict>
</plist>

Once of these may work. Granted I cannot test it because I just re-jailed my phone, but the properties are essentially CSS.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.