Incubation times for chickens and Guineas are a bit different. Also, you NEED to turn the eggs every day. Now, if you are going to do this manually it is not really a problem. However, Once the chickens start to hatch you WILL NEED a brooder for them while the Guineas continue to incubate and get turned. You will be hatching chicks in the bator while the Guinea eggs continue to get turned. This gets somewhat complicated, but can be done.
Now, if you have an automatic turner, you will need TWO incubators. One to take the chickens off the turner at day 18 and one to continue turning the Guineas. One bator with turner and one without a turner in it.
I use an OLD LG incubator for my chicks that need to come off the turner at day 18 and just leave the auto turner in the other bator.
Remember, you will need to have a steady humidity and temperature in BOTH incubators.
Once they are hatched (staggered) you can move them to a brooder that does not control humidity, but you will need a warm light on them to keep the temperature at about 90 degrees F.
The incubation period for a guinea fowl egg to hatch is 28 days, for chickens 21 days
Hope this makes sense