Welcome to the Zoom Community, @INA_Group.
Here's everything you need to know about Join Before Host:
https://support.zoom.us/hc/en-us/articles/202828525-Allow-participants-to-join-before-host
Note that if Waiting Room is enabled, only certain people can Join Before Host (people on your same organizational account, for example - if so enabled by you or an admin).
Note also that it's a good idea to have a time limitation on how long before the meeting people can join... but this presumes a "scheduled" meeting, and that people know how to tell when the meeting is supposed to start in their own time zone. (I know that is probably not an issue... but you'd be surprised how many people contact me saying "I couldn't get in!".)
Are you enabling the Allow participants to before host on the individual meeting?
I'd check there to be sure... you might have already done this, but if it's checked and it's less than 15 minutes before the meeting... anyone should be able to enter the meeting as long as Waiting Room is not enabled for the meeting.