Time spent picking in Greenfield is reported as impossibly high. For example, if I'm on the clock for 7 hours one day, Greenfield will report that I spent 10-11 hours picking. That's impossible. This causes the UPH to be calculated much lower than it actually is. It's a broken metric.
It's counter productive to wait unless you are just trying to play to the metric. There can never be a guarantee of how many loops around the store need to be done as there is always the possibility that an item isn't where it should be on the floor and you'll need to loop back around to see if it's unlocated in the back. If you are waiting 10 minutes for another order to drop, that's 10 minutes less that you have to look for things before INFing. Quite often the difference between being green and not being green is properly managing time to maximize how long you have to look for things, not just on your current batch but also on orders dropping in while you are working on the current batch. In that regard, it's always better to start picking as soon as possible after an order drops even if it's only one item.