How to schedule Tentative Events on iCal

Calendar on a Mac does not have a tentative status for the event, and only Apple knows how its software will be developed. The closest Calendar gets to a tentative status is a 'Maybe' response to an invitation sent to potential invitees for an event.

There are three options for a response to an invitation: Accept, Decline, and Maybe. If the latter is chosen this is represented in the event in Calendar by a question mark in an orange circle beside the name of the invitee.

Apart from that, the answer to your question is no.

Your question suggests that you think it might be useful, and Apple invites feedback at Feedback - Calendar.

Calendar on the Mac as far as I can recall has never had a 'Tentative' status for an event which I am told is a feature in Outlook in Windows. Creating a tentative event then inviting people to something that may or may not happen seems to be a very messy way or organising something. Apple has designed the calendar so that the attendance can be tentative, not the event itself.