This is probably just me, but they're young and so close in age you can probably just toss them in together with minimal issue.
If you want to be more cautious, then a wire divider for a day or two in between the two groups, but chicks are generally pretty accepting of new chicks.
I agree with the above. At that age, they're so close in size that they should be fine, even if put together immediately. You may wish to be more cautious and put them in a "see/no touch" arrangement for a few days, and mix them when you have some time to observe them. It really comes down to how the chicks behave when put together, and only observation will tell you that.
We've mixed chicks that were two weeks old with three day olds with success after watching them in the brooder. They were, however, Silkies, so that may have had something to do with smooth integration.
Do what works for you...