Presumably these are lightning invoices, which can resolve in milliseconds.
Lightning is just an off-chain out-branch, which will eventually be re-integrated onto the main blockchain (based on its original funding/terms). The benefit of this is that single entities can branch off the main blockchain, which is limited in its total blocksize/capacity.
The only limits are those by the handling lightning institution. This differs from bitcoin's main public blockchain, which rewards/creates approximately six blocks /hour, each with a limit of just a couple megabytes.
It seems like a major issue when dealing with multimillion dollar transactions.
Let's say I have 1 BTC. I buy something for 1 BTC on lightning network A. Simultaneously (within nanoseconds) I buy something for 1 BTC on lightning network B. I never plan to use BTC again (or if I do, I will use a different wallet, etc.) Do I just get two purchases? Is there a meta-network clearing house, and if so, why are there many disjoint networks.
Or do I need to have moved my BTC into the lightning network A or B before I spend it?
You have to lock your bitcoin on the main chain in a script that shares the bitcoin between you, and another lightning network user (typically a hub)
The trick is that a lightning transaction happen by signing transactions to the other party that changes the way the bitcoins are split, without broadcasting it to the main chain. You only broadcast to the main chain when you want to unlock the bitcoin. Broadcasting an earlier transaction will result of you losing the found because subsequent transaction contains secrets that allow the other party to take them.
Basically a Lightning connection (or channel) is two parties locking up some money (in any amount and any split they want) and then repeatedly re-agreeing on what the current split is. At any time they can close the channel which unlocks the money according to the latest agreed split. It's cleverly set up so that if either one cheats (by trying to finalize an earlier split), the other one gets to overrule it and keep 100%.
The most money that can be transferred is when the split is 100% to one party. Then you need to finalize it and create a new one.
It's not as magical as its proponents think. It is better than the base protocol in some cases - if you have connections and money. The sender having to lock up actual money in advance, in the maximum amount they can foresee sending, is a real buzz killer for the sender. And if the sender is some central relay - if you want to receive via a central relay and not peer to peer - you'll have to convince them why they should do that. Usually by actually prepaying, in real bitcoins, a few percent of what you want them to lock. Which is more than the transaction fee for a nontrivial base layer transaction.
To date, my own full verification node rejects all lightning/segwit blocks, until a concensus level of 6+ is reached. I think both were BIP errors, but rejoined the main concensus network ~2018.
Also participated in the O.G. bitcoin hardfork, back in August 2017, supporting the larger_blocks camp (but now mainchain, only).
Not on the lightning network. Fees are used to incentivize or disincentivize routes across channels.
> The institution handling this offchaing lightning branch can implement fees in whatever structure you agree to transact, including percentage based.
No institution is needed. Even if one is used as an intermediary, when using lightning non-custodially, the economics of lightning are such that fees are determined by the nodes in the payer's desired route. If it's a custodial transfer from one user to another, no routes are needed.
I imagine the seconds to pay won't be true - if they are exchanging emails and inspecting boats it's going to be an hours to days long process.