Issue with time slots

My time slots are suddenly registered differently in the booking calendar, namely one hour later. For example my time slot runs from 3 p.m. to 4.30 p.m. Booking calendar records it as 4 p.m. to 5.30 p.m. in my bookinglist. So when someone makes an appointment at 3 p.m. it’s recorded at 4 p.m. in my bookinglist. How can I solve this problem?

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