When a Matter is set to "Not Billable" "Contingency Fee Based" "Flat Fee & Contingency Based" or "Flat Fee Based" all Time Entries will automatically be saved as No Charge Don't Show.
This allows you to track the time for your own records, however, it will not show up on any invoices.
You can choose to save Time Entries as No Charge, in which case the Time will show up on invoices but a 100% discount will be applied. This way the client can view what work was done, but will not be charged for it.