Wrong time at website

Hello,

our site offers making a reservations on different hours during the day. However, everyday, about 5-6 pm, system ‘switches off’ the reservations for a given day and shows reservations made by customers for the next day. This, what should be done automatically about midnight, happens 6-7 hours before. For an example: today is 19.2 and now (about 2 pm) i can see reservations made for today and this should last to the end of the day(18.2). However, about 5-6 pm today this reservations will disappear and system will start showing reservations for tomorrow (20.02.). How can I change it?

Thank you for your help

https://wordpress.org/plugins/booking-system/