Add divetime to date value

Hi, I translate your plugin in french how can I send it to you ?
Yes, I know that this plugin hasn’t been updated over 2 years but it would be very helpfull by adding the divetime with the divedate. I try to modify the type of date column directly in the table setting to datetime. I try to change the way you check the date values but I’m stuck in the code.
Thanks for helping.

https://ww.wp.xz.cn/plugins/divebook/