An extension for my worker was requested and they're saying that they don't have any timesheets available to enter just yet. Why is this?

Check the Contract Register Report to see if they are showing as having an active contract

For an extension to be processed, we require fully signed contractor and end client agreements, if we are awaiting on one or more signatures on an extension we are unable to process it. Once the fully signed extension documents are received it can take 24 hours to update the system.