It is up to the user (the server can't enforce or see) but clients will use a default value. 

For a long lifetime coin, this should be months. 

For the DIFFERENCE on transfer:

It needs to be long enough to get the backup confirmed in that time. Assuming a CPFP to bump fees to the required fast confirmation level, this can be a short as a few hours. 

However this becomes less secure for low value coins (where fees might be high in the future). 

Thanks for the reply:

So appox how many blocks is the timelock?



freetx

The backup transactions have an absolute timelock - so there is no way a previous owner can broadcast before the timelock. If the operator is shut down, the owner needs to be online when the timelock becomes valid.

bitcoin

Mercury layer AMA

tptrevethan

1. No - you don't need to be online - either for chain-watching or receiving. Transfers happen in a two steps operation: send and receive. But receive can be done at any time - don't have to be online at the same time. 

The backup transactions have an absolute timelock - so there is no way a previous owner can broadcast before the timelock. If the operator is shut down, the owner needs to be online when the timelock becomes valid. 

2. Yes. However the operator keeps and encrypted transfer message (which is just an encrypted blob to them) which can be used to recover the wallet if all you have is the seed. Obviously if the operator is shut down, you need the backup data. 

3. In case operator shut down, all owners need to wait for the timelock expiry, and make sure their backup is confirmed in the time window (using CPFP if necessary to bump the fee - wallets can be configured to do this automatically). 

4. We (Commerceblock - a UK company since 2017) will run a mainnet server - as a single entity. Obviously trust is required - which can grow over time as reputation increases from reliability. Anyone else can run their own. Federation is possible - current implementation would need to be extended. 