Is it possible to compare dates across rows?

I’m struggling with the following problem.
I’ve made a small system for a clock in a clock out, which tells how much money we’ll be invoices at the end of the month. However sometimes staff manage to clock in and out twice, which makes my end of month salary calculations in accurate.

I’ve been trying to think up a way to check if the same staff has logged the same date twice.
I’ve found a way that involves a sperate linked table where each row contain it’s own date and each staff has its own column with a bunch of look ups. However its very messy an inflexible and way more time-consuming than meticulously combing through all the clock ins at the end of the month.
Sofar I’ve come up short, I have the feeling it’s not possible, but is there anyone who has any suggestion?