Carmine is probably correct. If you have your security settings set to lock the T3 it will override the stay on in cradle settings.
Your setting the Auto Lock to 10 minutes will not override the power of the stay on in the cradle setting. The only way to override the stay on in the cradle setting is to totally turn off the security setting. This is a built in protection within the Palm OS and is consistent on every Palm device.
The intent is that the device can not be compromised ever and thus the 3 minute rule goes into effect if you have security set.
The 10 minutes your talking about is simply that you don't have to re-enter your password to gain access during the next 7 minutes that the screen goes blank.
If this setting weren't present - then you could leave your Palm in the cradle all day and anyone that walked by your desk while you weren't there would gain access to your info.