code for enable or disable submit button

hi ,

thanks for your time,

please tell me the code location for submit Button unable or disable,based on the time entered in ManageTimeSheet Lines:

newTimeSheet->i want to enable submibutton only when i entered hours, when i press validate check mark any one have any idea reg this

where i can find code location for anabling or disabling submit button

Thanks,

suresh

the above process is on ep site