Can several comboboxes be used to clock-in the different users at the same time?

I am trying to log in several users at the same time using combo boxes to make it easier for them to find their names and save time.

The usernames are located in the same Table and column.

I have no problem with the combo boxes displaying the usernames, but when I want to save the clock in time, the records are not stored for either of them.

Is it even possible to make a one-time clock-in for multiple users located in the same column of the same table?

Also, I was trying to do it using check boxes, but I'm not sure how to program that whenever they click on the check mark, the current time "NOW()" gets registered in the database.

I would really appreciate any help!