Challenge Period

The Scheduled Finalisation Time (SFT) is the time when an exit can be processed after its challenge period has passed.

Any exit must await a Minimum Finalisation Period (MFP) from the moment it is initiated. Exits involving fresh UTXOs are additionally subject to a Required Exit Period (REP). Both are set in the Plasma Framework contract.

The formal calculation for the SFT is as follows:

Exit type	Scheduled finalisation time (SFT)
Standard exits	SFT = max(exit_request_block.timestamp + MFP, utxo_submission_block.timestamp + MFP + REP)
In-flight exits	SFT = max(exit_request_block.timestamp + MFP, youngest_input_block.timestamp + MFP + REP)
Deposit *	exit_request_block.timestamp + MFP's

* Refers to a standard exit on a deposit-generated UTXO.

Parameters:

Parameter	Description
exit_request_block	The root chain block where the exit request is mined.
utxo_submission_block	The root chain block where the exiting UTXO was created in a Childchain block.
youngest_input_block	The root chain block where the youngest input of the exiting transaction was created.

Consider an example whereby the MFP and RFP are set to one week each.

For a standard exit, this would mean that the Scheduled Finalisation Time is one week from the exit transaction if the UTXO is one week old or more, or two weeks from the creation of the UTXO if the UTXO is less than one week old. The same logic would apply to in-flight exits but on the youngest input of the exiting transaction.

For a standard exit on a deposit-generated UTXO, the SFT would be simply one week from the exit transaction.

Getting the Scheduled Finalisation Time

We can look to omg-js to abstract this calculation and give us the Scheduled Finalisation Time of an exit.

rootChain.getExitTime({ exitRequestBlockNumber, submissionBlockNumber })

Under the hood, this function is calling the Payment Exit Game and Plasma Framework contracts to apply the logic explained above. It will return the Scheduled Finalisation Time (in Unix) and the milliseconds until that time.