There is no interval between checks; there is no way to measure the state of charge instantaneously. The monitor must continuously measure the current and calculate how many amp hours go in and out from the current and time. The amp hour calculations must be done every second or so because the amp hour display makes no sudden changes.
I haven’t installed my Hall effect meter yet; I’m really writing about my cheep shunt based battery monitor and assuming it functions the same way except for the method of measuring current. I would expect no jumps in amp hour display from the Hall effect monitor, too.