Thank them for asking
Treat the question as reasonable.
Give an honest range
Share the typical wait, not the best case.
Explain what affects it
Mention busy hours or urgent cases that take priority.
Offer a better time
Suggest quieter days or hours if they can move.
Offer to notify them
Offer a call or text when it is nearly their turn.
Say what to do if it changes
Tell them how to check for updates.