Hello.
Did you know that you can check somebody’s availability for a meeting slot before you book it in and expect them to be there?
In iCal, click on Available Meeting Times…
And it will show you this window…
…which will let you know the availability of everybody in your invitee list. You can even click the “Next Available Time” button in the top right hand corner to find a slot when everyone is free.
Similar stuff is probably also possible on Windows. Welcome to technology.