Two things lock time/expense entries within Tempest-Time.
An invoice has been generated for the client. If it is not End of Month, this is unlikely.
A timesheet or consultant invoice has been generated within a date range that includes the time/expense entries in question.
If your time/expense entries are locked:
Check to see if you have a timesheet or consultant invoice that needs to be deleted first. If you are trying to edit a time entry from 30 April, and you have a timesheet for the date range 16-30 April you need to delete the timesheet to unlock the time entry. Click on your existing time sheet or consultant invoice to edit it using the Edit Pencil. Click the red Delete button.
If #1 is not applicable, the time or expense entry is likely on a draft or final invoice. Check with your Tempest-Time administrators to see if the invoice is a draft, they can delete it so you can make changes to your entry. If the invoice has already been delivered to the client, it may be too late to change it.