I've lost track of the number of FT supervisors & managers I've worked with who've removed time from timecards. We had one guy that we nicknamed "Doc" -- short for payroll doctor -- that would subjectively enter time cards every day & remove enough time so that the sort met whatever goal it was attempting to reach. LP came in & took statements, checked the logs, confronted him... then slapped him on the wrist (now, Dr. Timecard ... don't do it again - or else!). Any employee that confronted him he'd challenge with 'I saw you [insert excuse here, such as spending 3 minutes in the bathroom] - you don't get paid for that, and if you insist, I'll follow you around all day and the second I catch you sipping water or anything, I'll fire you for stealing time.' Literally, the guy was a

and despite a pile of grievances, phone calls, letters to the state, you name it... he remained here until he moved on.
Today, it's still common for a supervisor to tell (not ask, not seek volunteers) an employee in the Input to walk to the furthest line in the building to go load trucks -- about a 3-4 minute brisk walk. And guess what? They dock five minutes from the time card.
We also play the game in which start time is listed as 3:55AM, the computer will show 4:00 AM -- and it's locked, so you can't change it, we'll start at 3:55AM (as scheduled), then get paid from 4:00AM because opps, they forgot about it. For the 1,000th time, because they're so super busy that correcting 400 time cards that just so happened to push their production into bonus territory slips their mind, right?
<sigh> Best advise is to keep track of your hours, each and every day.