About 2 weeks old is when they get moved to something larger. I will have a lot (up to 50) in there when they first hatch, but they have to get moved or separated into more bins as they grow.
I keep the lid about 3/4 to 2/3 over the bin. My body blocks the rest as I reach in to scoop them up.
They'll be a bit less flighty is you scoop them up rather than trying to grab them from above. They assume things swooping from above are predators.
They'll be fine in such a short period. I have two 50 gallon tubs for brooders. I have a clean one ready, transfer the chicks to the clean one, then clean the dirty one so it's ready for the next cleaning time.