If many of your clients live around the world in time zones different than yours, you can set notification emails to display both your time zone and theirs under Settings / Notifications / Client Notifications.  Note: If you allow clients to book without logging in, or the client has never booked online with you, the notifications will only display your time zone.

You may force clients to become registered users and log in, under Settings / Configuration / Advanced / Client Booking Limits.