Wedding rehearsals usually take about thirty minutes and are normally led by a wedding coordinator if you have one or by yourselves.
The rehearsal is practice for all who will be in your processional and recessional so that they will know where they will be, what to do, when to do it, and who they will be partners with.
Wedding rehearsals can include parts of the ceremony or music, but these are not a necessary part of a rehearsal.
You do not need your wedding celebrant present to run a rehearsal. However some bride and grooms really are nervous and wish for the celebrant to be present. If this is your case, don’t hesitate to talk with your celebrant about it. She/he can be available the day before to come for an extra fee including hotel accommodation if needed to stay nearby until the wedding day.