Squarespace announces orders but not the stock you edit yourself
One of those reaches the till right away. The other waits for our next look.
A Squarespace order reaches us as soon as it is placed, because Squarespace tells us about it. A quantity you change by hand inside Squarespace is a different matter: there is no announcement for that one, so we check every couple of minutes and pick it up on the next pass. Knowing which of those two you are doing explains most of the timing questions people ask about this pair.
In practice a sale on either side is handled quickly, and the only lag worth planning around is you editing a Squarespace quantity and expecting the register to know within seconds. If you run a stock take in the website admin, give it a couple of minutes before you trust what Clover shows. A small buffer on your fastest sellers covers the same window without you having to think about it.