I know I shouldn't do this, but I will assume that this is to allow some kind of service that needs the Internet access to run at specified times (like a mail server dialing out to upload/download mail?)
I'm not aware of a service that will do it natively, but you can set time based access lists that allow traffic only at specified times. Then you could define what is considered interesting traffic, set that to the type of traffic being generated by the mail server, for example, and create a task on the server to dial out at those times specified in your time based access list.
Check the following link on time based ACLs.
http://www.cisco.com/warp/public/707/confaccesslists.html#time