Here is Germany it usually takes a few seconds (less than 5 I'd say) - I noticed however that paying at Aldi Nord is very fast. They really do tweak the cash register speeds at Aldi...
Not only that, but the Aldi checkout operators are extremely fast at scanning products compared to other supermarkets (at least that has been my experience in the UK).
Because in Germany it's very fast
ALDI/LIDL are outliers here in Germany. Other supermarket checkouts like Rewe, Edeka, and Kaisers are slower at scanning items. So don't take the speed of ALDI/LIDL cashiers to be indicative of every supermarket checkout in Germany.
Overall, German supermarkets scan items faster than in North America, but ALDI/LIDL are really in their own league. I sometimes think they are faster to scan items than to drop the contents of the belt onto the floor. Impossible to pack in real-time!
Some years ago they punched in all items by number and were even faster.
The downside was that for the first months of your employment you were at home learning all codes.
I still remember that 515 were cucumbers and I believe 529 were 2.5kg of potatoes?...
I also just noticed the dual-conveyor model in operation at a newly-opened Lidl near me yesterday. ALDI here typically doesn't do that--most stores are set up to place groceries (and unfilled bags) directly into a customer cart, and have a nearby counter to bag your groceries at.
I assumed that there must be some further process that it goes through, between telling the credit card reader that it is completed and Monzo getting informed.
Monzo take advantage of this to enable their realtime notifications and related features, otherwise Monzo would receive the notification of the charge up to 48 hours later which would be a significant harm to the UX.
Old stores, especially small mom-and-pop ones, are still stuck with readers built a decade ago, or with modern readers uplinked by POTS. I recently helped my vet switch from an old POTS terminal to a brand-new, DSL-linked one; the speed difference is huge.