It's OK but it is better to separate the ones that are to hatch on day 18 from the not so far along ones. I now have two homemade bators, so on day 18 for my EE I took my Buckeyes out and put in my smaller bator until after the hatch.
You still have to turn the less developed eggs and you aren't supposed to open the bator for the last three days and you have to have higher humidity for the last 3 days.
I am going to have 3 hatches in a row 2 wks a part (God willing) because I am collecting EE eggs now to put in the bator once my first set hatches (hopefully by tomorrow) and set the next batch by Friday.
If you need a second bator you may want to consider making one. There are plenty of people here that can help you. I use a version of the Matilda that I got on this site.