Due to historical reasons, Wink doesn't always name the fields verbatim the same as inside ServiceM8.
Here are the date fields in Jobs:
Opened Date: This is the date when the job was created in ServiceM8.
Completed Date: The date when the job's status was last changed to 'Completed'.
Quoted Date: The date when the status was changed to 'Quote'.
Accepted Date: The ServiceM8 job was last changed to 'Work Order' on this date.
Invoice Ready Date: When the job was marked 'ready to invoice' in ServiceM8.
Invoiced Date: The date when the invoice was emailed to the client. If no email was sent then the date will not be populated.
Paid Date: The date when the final payment was received and update on the job.
Rejected Date: The job was last moved to status 'Unsuccessful' on this date.
Estimated End Date: This is the date of the last appointment currently scheduled for this job.
First Payment Date: The date when the first payment was received for this job (if there are multiple payments).
ServiceM8 does not record every instance when the above happens, only the last instance. For example if a job was move to Worked Order, then Completed and then re-opened back to Work Order, the "Accepted Date" will be the second time it was moved to Work Order.
Similarly editing a Completed Job appears to 'reset' the Completed Date to the current date.